Pass protector upgrades are great for rounding out guys who are already very good run blockers. It takes a ton of XP to move the needle eventually. Getting a power OL's PBF into the high 70s/low 80s can make a world of difference when facing good speed rushers.
When developing them the basic question is do you build on their strengths or try to shore up their weaknesses. If my guy is already in the low 80s for RBK and PBP there's not really much to be gained by further development of those attributes unless he's a superstar. Getting an Agile or Pass Protector upgrade or two can make them a much better player.
OL are pretty fluid in this game and it makes them one of the few positions that's actually fun to scout and develop. Draft classes feature Agile OL with elite STR and Power OL with decent mobility. BPA trumps scheme fit when you are looking for them, and there are starting caliber players available in late rounds if you know what you are looking for (STR, RBK, PBP, PBF - everything else is gravy and can hopefully be boosted by development).