With the new interpretation of Rod of Carnamaegos, this might be much easier to achieve. Not good at probability math, but a full bag of each type, a rod, plus an Olive may be much more efficient in getting both sides out than you would with favors.
As of the Feast of Hemlock Vale Investigator Expansion, there are 26 Tool or Science assets that exhaust.
Strange Solution, Cleaning Kit, Cryptographic Cipher, Fingerprint Kit, Matchbox, and by extension Quickdraw Holster all have uses that are spent when exhausted and need help to be replenished. Readying these assets doesn't increase the value of the asset, only increases the tempo of the asset. Spending two resources and an action to slightly increase the tempo of an item is somewhat counterproductive, so these are not great choices.
Ice Pick (3) and Lockpicks (0) are cards that you expect to discard fairly quickly, so taking the time to attach this certainly isn't worth it.
Dr. Charles West III, Dream-Enhancing Serum, Pocket Telescope, and Mechanic's Wrench are all cards where the exhaust effect isn't the main reason you bring the card, so readying the asset probably isn't worth the cost of Fine Tuning.
Darrell's Kodak and Grappling Hook are not going to be reliably useful multiple times in a round. It might be worth considering for certain parties or builds, but isn't an obvious pick.
So this leaves us just 11 cards to examine.
Great Choices:
Chemistry Set is one of the better cards to ready. If you're taking the time to build around it, Chemistry Set is a very efficient way to investigate, yielding a bit of extra economy and the occasional spare clue. Most seekers are hoping to investigate twice a turn, and for those who are typically testing book v shroud, doubling down on Chemistry Set will likely be an efficient use of their time. Just be wary of losing both cards to a fail by two if you can't adjust the result.
Of course, if you're bringing Chemistry Set, you should also be bringing Steady-Handed. Refreshing both together is very logical, allowing you to adjust both checks to an even number, and avoid throwing the set out to a bad pull. As of right now, there's not much else for Steady-Handed to adjust, so this is certainly a lower priority.
Lockpicks (1) is one of the best uses for this card. Yes, it discards when the uses are spent, but it's not unreasonable to expect that you'll get 10 or more refreshes. A rogue clex-leaning-cluever can legitimately make this their main engine for when there aren't any enemies. Mariner's Compass and its upgrade are similar for survivors.
Empirical Hypothesis is going to be one of the strongest targets for Fine Tuning. If you haven't put any experience in, this will likely be a second card most turns. You do need to initiate two tests to get the full value, but most seekers are investigating 2-3 times a turn, so it should pay off more often than not. The value goes up if you sink in some experience; with Peer Review, you're all but guaranteed that one of your allies will find the second oversuccess, and more likely to convert the charges into value.
Finally, Pocket Multi Tool is a great choice. With just a bit of XP, this is two resources, 1 XP, and an action for a free unexpected courage once per turn. With Spring-Loaded, it turns into a free Lucky once per turn.
Situational choices:
Lab Coat isn't likely to be worth tuning up, since it's incredibly unlikely that you fail two tests in one round by exactly one. The most notable exception to this is if you're frequently testing at just below a critical value in the chaos bag (frequently testing at +2 when the bag is majority -3, for instance). If that's the case, then you can adjust on a per-scenario basis, although it's going to depend so heavily on the shroud values that you probably shouldn't make this your main game plan. It can also be cute if you're frequently testing against a shroud of 1 for guaranteed success; see The Skeleton Key.
Survival Technique is probably tough to use multiple times per round to great effect. There are probably cool combos that you can attach and pull back multiple times per round, but they're too complex to analyze in this little review box.
Backup choices:
Microscope can be ok, although if you're building around Microscope you certainly want to upgrade them as soon as possible. You can attach this to your Microscope in the interim, but shouldn't invest the XP in this card unless you have another asset to fine tune once you can get the good Microscope.
Ice Pick (1) is a small skill boost once per round. Doubling this is decent, but similar to Microscope, you are probably taking this on the way to upgrading this, which means you need a backup target for your Fine Tuning once your deck hits its stride.
This card is bonkers for parley decks. For only 2 resources and an action (and a slot that you were propably not going to use) you get to "add" to your hand all your parley events in your discard pile. For decks that don't have a lot of draw this can be extremely valuable. Snitch, Vamp, Grift and Beguile are the prime candidates for Eldritch Tongue. Nevertheless, any other parley event should be fit. I have found myself always happy to play this card, give it a try!
If you're able to run Pelt Shipment and take Down the Rabbit Hole, it cancels out the increased experience cost to add new cards to your deck for at least one card. If you're crazy enough to run the second copy and have only the two Pelt Shipments in your hand you're back at a net gain for experience, right?
Damning Testimony has few investigators who want this because of the book requirement in Rogue. Without the Seeker 0-5 Rogue 0-2 Investigator, currently the only people who really want this are Trish, Finn and Alessandra, because they all have 4 book in Rogue, and also all benefit from enemies being alive already. Trish baseline gets an extra clue, Finn likes Evading, and Alessandra wants to Beguile enemies all over the board.
The closest comparison for this is actually Fingerprint Kit, because that is a high cost limited use item that gets you 2 clues in 1 action. The main value here, is that Damning Testimony gives 2 clues in 1 action in Rogue, which is kind of the best clue efficiency Rogue can ever get. Normally we look at Lockpicks or also Thieves Kit. Rogues' main value was getting additional actions to use, but Lockpicks was always once per round. Damning Testimony is also once per round. But the pros?
Pros:
Cons:
While there are 6 upgrades you can take, I personally only think 2 are of serious value, for 4 xp. Blackmail, to get a +2 to the test so you pass, and Fabricated Evidence, so you get 66% more value from your item. for 4 xp then, in the 4 investigators i mentioned, you're testing at 6 to shroud which is a great start to be in and 5 times you can get 2 clues over 5 rounds. This is really good considering its 1 handed, so you can still run something else in the other hand, be it a weapon, or a different item to help investigating such as a lockpicks or a thieves kit. or another Damning Testimony. Damning Testimony also goes up in value for quite a few scenarios if you know them, such as scenarios with patrolling enemies (Fortune and Folly), or chasing enemies (most of the Innsmouth campaign, that infamous train scenario)
Combined with Lockpicks to have something to do with your other 2 actions, I think this is incredible value for XP and Resources. The main problem to overcome is having enemies at the correct locations, which can be a problem to manipulate, but not insurmountable. Rogue now has 2 cards with Bonded enemies they can force into play (Crystalizer of Dreams, and Bianca die Katz). Trish can use Existential Riddle on Hunter enemies so they keep moving. Transmogrify can be used on 1 location to lock an enemy down. Alessandra has Beguile which lets her just move an enemy. Disguise Kit and multiple other effects can lock an enemy down for multiple rounds. But if you're looking to get some clue efficiency in Rogue, I think Damning Testimony is worth the run.