Only trick is, in play, that doesn't actually fit with what is happening.
The range between Sanity scores is so small, and overwhelmed by the d20, that unless we're talking an 18 vs a 6, (and even that's only a +6 spread), there isn't much, if any difference between two characters. Whereas having that much of a spread in any other stat is easily noticeable. A 3 point spread (say a 16 vs a 10) only matters about 15% of the time. That 16 San character fails slightly less than the 10 San character. And, note, there's nothing else that modifies the check - not class or background or anything. Additionally, if you play with point buy, like I do, then everyone has virtually the same San score anyway - maybe a +1 on the check vs no modifier.
And, remember, this is quite different from what
@Imaro is saying in that a high Sanity score lets you understand the ineffable better than a low Sanity score.
Which brings around my other major problem here. It's entirely a binary system - either you fail on a San check or succeed. Fail is an entirely random effect from a table. Succeed and ... nothing. There's nothing the players can do with this. They can't use it in any way. It's not like every other stat where having a good score lets me succeed on checks that I can initiate - I want to jump far, have a good Str score. I want to be good at noticing things, have a good Wis score. But Sanity just sits there like this lump.
