I really think that the team cannot go wrong by getting an O-linesman every single year. They are ALWAYS in demand, so pick one that isn't a project, coach him up, and then either cycle him into the line-up -- first string or second -- or use him for trade bait. EVERY team, it seems, is always going to need an O-lineman at some point and he who has stock-piled the crème de la crème will be in the cat-bird's seat. I just don't see any downside to having good O-linemen on the team, at least one or two per year. One thing for certain -- at some point almost every O-lineman is going to be hurt. If your team has a couple in reserve, well, then you can trade for players or draft picks.
Of course, this is probably a simplistic view of a complicated situation; namely, the team is comprised of more than just o-linesmen.