Up to 100 they work. Past 100, you're pretty much wasting your time.
I suggest that once you hit physical level 50, keep your dex, str, int, and pie at 86 and your vit and mnd at 80. Then use conversion traits and gear's innately appropriate stat boosts for the rest.

There is next to no point in getting over 130 of a given stat. There IS actually a big difference between 40 and 100 of a stat though.