We haven't found all the Curios yet and they are still getting Balanced but its clear that people are boiling the data down to a simple value, LP per Hour per Attention (LP/H/A). So far their is a surprisingly broad range here, from lows in the 20's to highs of nearly 600 for Ant Empress (and that's after it was Nerfed). It's likely that this range is going to narrow as we have seen Nerfs to the uber items and buffs to the weak ones but it won't disappear completely, this is certainly intentional as their should be a spectrum of newbie stuff and more rewarding elite curios.
But what I fear is that after all the data gets crunched the great surface diversity of Curios is going to look a lot shallower, people would just equip the highest LP/H/A items they can manage, the system would just be a simple Spread-sheet-optimization. What could really spice up the Curios would be a secondary bonus from each Curio type that applies while it is being studied, now the player has another aspect to consider and if each Bonus is unique it breaks the simple spread-sheet-optimizing mind set.
Bonuses could be the typical +Stat or +Skills kind of stuff we are familiar with but I think some more interesting stuff could be done. One useful Bonus set could be to speed up the hourglass on a number of common activities. For example Cat Gold which people found was rather mediocre in LP/H/A could make stone chipping faster, something quite useful for newbies looking to do a lot of paving. Or Auroch Hair could make the painfully slow Animal domestication process faster (one less Quell?). Wood Shavings half the time needed to make boards.
You see the theme here, the Curio helps us perform the activity it would normally be collected under.
Other types of effects could be more subtle, with a fish Eye you will see the fish Nodes more easily (animation occurs more or is continuous?). The Strange Crystal from Mining very slightly reduces the chance of a Cave it. Spider Web gives a 50% chance to get Double Spindly Taproot. All useful not not overpowering things.
Lastly their might need to be some means to prevent endlessly milking these effects by removing and re-adding the curio, while the player would effectively be delaying LP gain I'm not sure that would be sufficient cost. It might be necessary to add something else. One possibility is causing a small 5-10% quality loss to a Curio that is removed from Study (the item is naturally less Curious now that your familiar with it). Another would be delaying the Bonus until the Curio is some decent percentage studied or to use an escalating Bonus that starts at zero, a bit like how Tea worked.