I personally think its worth the risk. Drew Brees was a risk the Phins didn't take.
If I'm Manning I don't want to play for the Colts. They have an old, depleted roster and will be re-building. I think the Phins are an ideal fit. Solid defense with younger veteran players, young offense with good receivers and 2 premier O-lineman and the 8/9th pick in the draft to fix one the few holes on the team (and an owner who is willing to spend in FA to fill other holes).
Quite frankly when I look at the upcoming SB, what really separates the Pats/Giants from the Phins is a QB. I would argue that the Pats have more holes on their team (aside from QB) than the Phins. They do have a coach that knows how to mask their talent deficiencies (especially on defense) and a franchise QB. But make no mistake, they have plenty of blemishes.