If you did this trade, and planned to get your center by trading some combo of Scal, Tony, House, Pruit and JR - it kind of makes sense.
Rondo, Miller, Pierce, KG, Perk - if Miller bounces back from an off year, then he can replace Ray Allen well. He's got decent height for a SG, and can play SF in a pinch.
Foye becomes your combo guard off the bench. Gomes becomes your combo forward (replacing Scal), and presumably they pickup a Center in the trade. Powe's out for most of the year but eventually he comes back too.
Lets assume House stays, Pruit walks, and the trade is Scal, Tony, and JR for a big.
Rondo/House
Miller/Foye
Pierce/Gomes/Walker
KG/Powe
Perk/New Big
Pretty much depends on who the new big man is if the team is better it really all comes down to how good Foye is off the bench. If he can be a great 6th man, you are probably better off than with Ray. If he's just okay - then its a waste.