I love the curio system for its uniqueness and the flexibility of play it allows. With that said, a lot of curios are just unused as of right now, because their LP/hr or xp/hr cost is not worth it. Increasing the the LP/hr of these curios won't help solve the problem, however, as it will just introduce new curios which are comparably the worst. To add use to already existing curios which currently serve none, I propose an expansion of the curio system to include different types of curios which serve more ancillary purposes.
Basically, some curios, rather than providing a straight-forward, good LP/hr, would be worth studying because they provide some other benefit making them worthwhile. Here are a few examples I could come up with:
Enlightening curios
These curios would provide very little or no LP/hr, and would likely be studied somewhat faster than most curios, but would instead, upon being studied, confer a temporary bonus to the user. This could range from raw stat boosts to specific boosts tied to the activity the curio is derived from. Increasing quality would increase the time length of the buff provided.
There are a myriad of curios which could be used like this; a few examples could be the wondrous woodshaving, which upon being studied would provide a temporary boost to the amount of boards one can make from a single log, or the strange crystal, which could provide a temporary higher chance to find bigger/more naturally cut gems, fishy eyeball could improve catch chances, etc.
Priming curios
These types of curios provide little or no LP of their own when studied, but rather, upon finishing their study time, one could right-click it to attune it to another curio in study. This would then confer a percentage bonus to the curio it is attuned to, such as an increase in the amount of LP gained, a reduction in study time, mental weight, etc. Removing the curio to which the priming curio is attuned from study would remove any benefit provided (to avoid passively buffing curios on alts). Increasing quality would increase the magnitude of the benefit provided. (E.g. a priming curio which provides a 25% base LP increase at Q10 would provide a 50% increase at Q40, and so on).
This type of curio could be especially useful if one wanted to get the most out of rarer curios, especially ones which give very large amounts of LP, like troll skulls. An example of a curio that could work like this could be the crude idol.
Collective/set curios
These types of curios would provide middling LP on their own, but would confer a greater bonus if they are paired up with other curios that match their set in the study. The bonus could, again, be higher base LP gain, lower mental weight, lower XP cost, etc.
The benefit of these is rather straight-forward, and there already exist a few curios in the game which would naturally fit into sets of sorts, namely the straw/porcelain doll, the tin warrior and the bronze steed, the seer's items, etc.
Leeching curios
These curios would not progress in their study time simply through time passing. Instead, upon putting them into a study interface, they would highlight a number of slots in the study. Putting other curios into these slots would induce a debuff on the curio put there (lower LP gain, higher mental weight, etc.) and lock them in place. The timer on the leeching curio then starts running as long as another curio is put in the highlighted slot, stopping when the curio put there is studied. For the leeching curios with more than one corresponding "leeching" slot, each slot provided with another curio would increase the study speed by 100%. Thus, some leeching curios would provide a worthwhile benefit only if supplied with a sufficient amount of curios, and there are opportunities to try to calculate whether sacrificing part of the benefit of the other curios would be outweighed by the benefit received by the leeching curio.
Slotted curios
These curios would have comparatively very high mental weights and XP costs and only provide middling LP/hr. They would, however, allow the placement of another curio on top of them, essentially allowing to curios to fit in one slot. Essentially just cheese if you have high stats and want a bit more space to stuff curios in at the expense of XP.
Unfathomable curios
These curios would provide very high LP/hr bonuses at the cost of very high mental weight and/or XP cost. Furthermore, they would inflict a wound for as long as studied, perhaps a Concussion wound, but it could be a new and meaner wound. Higher quality provides better LP/hr as normal, but also strengthens the severity of the wound inflicted. When the curio is finished the wound would slowly heal on its own, but it can be treated with various ailments.
These curios are meant to provide a slightly risky but rewarding option for the user. Furthermore, it's meant to provide a way to use some of the healing items in the game and introduce some way to get damaged as a craftsman who isn't introduced to a lot of danger otherwise.
Of course, a curio could pertain to several of these types and creating interesting dynamics; a priming curio could be part of a collective curio set, providing a stronger bonus to an attuned curio if all priming curios fromt the same set were attuned to it, a slotted curio could turn unfathomable if something were put in its slot, etc.
These are a few that I came up with. If anyone has other ideas, it would be neat to see them posted as well.