As far as 2.0 vs. 2.16, I haven't seen any side-by-side benchmarks, but I would say that the difference is going to be minimal. The only reason would be just to brag about it, IMO.
The extra video memory might be useful in the long run, but for today, I wouldn't say that it's terribly important. Just remember that more VRAM isn't as important as the card itself. Different cards have different capabilities and better or worse processors. The significance of VRAM alone is small, and Apple sells 128MB and 256MB versions of the same Radeon X1600.
Check Dell for monitors, I'm sure that you can find a 19" for under $350, especially if you search for coupon codes.
Cheers,
reality