I am sure he will spend the rest of this season, all of next season and the beginning of the following season in AA. No reason to bring him up to AAA before hes 23. Maybe the end of next season, but no sooner. A good season and a bit in AA will be good for him for development sake.
With Beckett,Matsuzaka,Lester, and Buchholz likely to hold down the rotation for the next few years( barring injury, trade, ect). Theres only going to be 1 avaialbe spot in the rotation, likely to be filled by a Veteran. Bowden might claim the spot, but he might also become expendable in the right trade.
Just throwing this out there, but say the Fish Hold on to Miggy until next season, Maybe the Sox( who will be looking for a 3B to replace Lowell, or an OF to eventually replace Manny) Put a package together front lined by Bowden. If he has a good year this year, and next at AA his value will be exttremely hi. Not sure who else you include, by any package involving Bowden to start is nice.