The problem with prerequisites is that they tend to be a balance against access to powerful features. If your stat is high enough, you can take the powerful feature, and, as a result, are *extra* powerful. Not only do you have a super high stat related to this powerful feat, but you have this powerful feat as well which benefits from your super high stat. A double whammy that builds towards breaking the game.
Part of the problem is that when the player reaches that next modifier, they are greatly rewarded and compensated for the time until the mod increase. The real issue is making the incremental step not feel punitive. Maybe, all it takes is a modest bonus to say, "Here ya go, well done." Let's brainstorm some potential solutions. Each of these solutions would improve per point of ability score added. A second solution is to provide benefits for every point above 10 (although none of the benefits below make use of that stratagem).
- Carrying capacity. If encumbrance were made fluid and simple enough that most groups didn't overlook it, the strength stat would remain important. To make encumbrance not overlooked, it'd also have to be less punitive than it is now.
- Not sure. Everything I've come up with feels like it is probably too powerful.
- Languages. Perhaps a more robust language system could be put in place that rewarded incremental investment in cunning. Characters receive points equal to their cunning and (unless they have an exceedingly low cunning) have to be fluent in at least one language.
- Rank 1: I sort of understand it
- Rank 2: I sort of speak it
- Rank 3: I speak it
- Rank 4: I speak it and read it/write it
- Rank 5: I'm fluent (i.e. no accent)
- (perhaps) Rank 6: I can mimic other native accents
- Hit points. Vitality increases hit points at a 1:1 ratio. This also increases Bloodied.