Having just submitted a 0.5138 score hopefully due to some bug I haven't tracked down yet, I'm voting in favor of back submittal. :-)
I don't think more than a few are needed.. 2 or 3 maybe?
On the other hand, this will upset the balance that is causing the conversation in this thread: http://www.heritagehealthprize.com/c/hhp/forums/t/815/hidden-rules-for-team-mergers/5338#post5338
Namely that, when merging teams, the combined team can't have more submissions than they would have been allowed if they were one team the whole time. Queuing submissions or allowing back submissions is going to result in higher submission rates and will further limit the ability of teams to merge later.