Price is under control for 4 more years, by then, pretty much every prospect with upside will be in the majors. By then, they will have hopefully signed a FA starter. By then, Morneau will be gone, and they'll likely use that money on a starter or a 2B/SS. This isn't about this year, nor is it about rushing.
Sure, his value could rise, it could also drop. He could be the best HR hitter ever, or he could barely make it in the majors. There is risk in every move. What I would not do, is suck last year, suck this year, suck next year, and suck the following year, all because I would not sign legit MLB starters, or trade prospects for proven veterans. If you really think they should give up until 2015 or so, why not trade everyone over 28 right now?