Here's yet another suggestion (hey if nothing else all these postings will get me to the next stage - lol).

I think once a villager has mastered one skill, they should automatically become adept in any other skill they attempt. This would greatly speed (I hope) the process of mastering multiple skills.

It's kind of like when you're in college, once you get a masters degree in one subject, you don't have to go back and redo all the prerequisites if you want to take on a new major, you just jump right into it.