This is pretty self explanatory, the 3500+ has more clock cycles and is even labeled as a higher performing processor, therefore it will perform slightly faster in every area of processing when compared to the 3200+.
As for is it worth it, it depends. The 3200+ can be bumped up to 3500+ pretty easily even if you have no idea what you're doing. If you simply want the better processor out of the box and don't mind paying more, get the 3500+. I would personally take the 3200+ though.
Intel C2D E6320 / AMD Athlon X2 3800+
Gigabyte 965P DS3 / DFI nF4 Ultra-D
2GB OCZ Gold PC2-6400 / 2GB OCZ Gold PC4000
eVGA 8800GTS 320MB / eVGA 6800GS 256MB
150GB Raptor / 74GB Raptor
2x500GB / 320GB
OCZ GameXStreme 850w / OCZ StealthXStream 600w