So a pitcher with 30 velocity, 50 GB/FB will do worse than a pitcher with 30 velocity, 85 GB/FB?

Depends on other factors, all other things equal, you would expect the 85 GB/FB would have a lower Hr/9 rate, and hence a lower career ERA. On the other hand i I've got players with a K/9 about 6 and GB/FB of about 20 in Durham have season ERA's <3 so it's not a full gone conclusion.

While all the ratings make the pitcher's core value.....as Crump says, ballpark factors into it, defense factors into it, etc.  The great part about this game is while everyone can read and see good ratings, the true separation between successful and not successful happens when people can see all the factors, such as your entire team, the health of the world, the ballparks, NL or AL, etc and make a good assumption that certain blends are going to work to your advantage.  Sounds silly but sometimes it really is a gut feeling putting together a good team.  By good team I mean....anyone can stock highly rated players and play well, make the playoffs etc.  But those that continually win division championships and/or world series titles are those that see a little deeper and create a good blend.

I have made trades that other owners have wondered about, but have made them for a certain quality that I need to round out a team, a quality that standing alone may not look like much, but when coupled with all of factors create an advantage.