Would I be better off going for an i7 build?

For your usage, no. Ddr3 is still at least double the price of ddr2 in the usa. Socket 775 motherboards and cpus will be around for years. The current recession will cause a buildup of inventory. Core i7 is a good product, but you'll find much better deals for less than half the price on the core2 duo stuff. The best core i7 deal was a dell 920 complete system with 23 inch monitor for around $1000 a few days ago. It's expired now. Take a look at some benchmarks; Intel is a smart company when pricing their new stuff. The low end core i7's are similar in performance to some high end quad core duos, and both are priced similar. But it's the motherboards and memory that cost more.

for a year to 18 months the nehalem will not be worth it.

if you won't play crysis, don't get a core i7.
the additional money you will add should get the best video card. either a
4870 x2 or GTX 280.