The "De Vermis Mysteriis" card seems very strong. The card does not have any rules for discarding after use. Is it really possible to keep it an improve a skill round after round? Combined with some sort of sanity replenishment it seems almost too strong.
Short answer: Yes.
Longer answer: Note, you can only improve each stat a total of two times (thus there's only +1/+2 tokens). You also cannot perform the same action in a round (so can only use the item once a round). This is also balanced by the check, which you may not pass.
So yes you can spend 10 rounds maxing out your guys stats (if you roll well/pass the checks), but likely you'll need to rest as well, so you've basically spent 10-11 rounds doing nothing if you do that. Since the difficulty of the game is dependant upon the # of players and things happen every round, taking this action especially repeatedly actually makes the game MORE difficult for your team (in my opinion, it'd be better to have no player playing doing this for 10 rounds and the game be easier than to have a player doing this).
In my limited experience with this game, if you have 10 rounds to sit around doing this, you probably need to find a harder game for yourself (or you're being carried);) I have not had such a luxury in multiple play attempts. I have had this item and recall using it when my health is down but my sanity is not and I'm going to rest anyway or when I have a skill I want to bump to try and forward the game.