It's a shame that Serra was forced to fight GSP back-to-back like he did. GSP is a caliber above nearly every other WW fighting, and Serra had to fight him twice in a row, w/ no reprieve or chance to grow.
Meanwhile, GSP was able to hone his wrestling skills against Kos and Hughes before fighting Serra again.
Not that Serra would have won, mind you, just that he was at a a severe disadvantage in that second fight, far greater than if he had fought two fights against tough opponents, and then fought GSP for the rematch.
As for Serra fighting again, he at least had Hughes, and would love to see him in a rematch against Shonie; they're both past their prime, and I think it would be a great way to send both out to pasture in the UFC.