You could throw new bearings in it for a few hundred bucks if you do your own labor. The question is if it has any other problems. Kinda suspect since engines don't generally develop these types of issues without some kinda of abuse. If you end up doing a complete rebuild (machine work, pistons, all gaskets etc) it probably wouldn't end up being worth it.

2003 and 2004 don't have these problems... well... not nearly as many documented cases at least.

my 2004 is an oil burner

i have to fill in 6 cans of oil every 2 munthes

I dont know if it is the pistons rings or the valves seals

If owners were willing to loose 8-16 HP in a rebuild the 3.5 would be a wonderful engine.

If this is a front engine you're talking about, it is DEFINTELY not worth buying a bad engine in need of rebuilding for $500, as you can find a perfect working order FWD VQ35 for $500, one needing no rebuild. I am not sure on RWD VQ prices as I have never priced one. check http://www.car-part.com