Of course, you'd rather have a proven name in the middle of the line, but I really think the Rams should be fine with either Romberg, Incognito or Setterstrom at center. Romberg and Incognito have both had starting experience there, and Incognito's turn at center in 2006 was a solid performance. Romberg's 2007 stint at center is hard to judge since the line crumbled on both sides of him early on.
Upgrades, good ones, at one position on the o-line tend to make it a much better unit. Obviously, a healthy Pace will be like having a new LT after 2007. The Jacob Bell signing should do wonders for the middle of the line AND help improve the quality of play right next to him at center.
Finding a starting center should again be one of the more interesting position battles at Rams training camp this season...wherever that camp happens to be.