It the i5 has done everything I needed it to do and is very quick. My needs sound similiar to yours and going from an hp with a pentium or even from my macbook core 2 duo up to the I5 was phenomenal.
What you might do is go to bestbuy. Ours has an apple section setup with 21"/27 " iMacs, macbook pros, airs and minis.
However the difference in the i5 and i7 from my understanding is that the i7 makes virtual cores. So if its the quad core one it utilizes 8 cores with hyper threading but if you aren't going to open up photoshop, final cut, protools, logic, iTunes, and safari at the same time you will probably be happy with i5.
The price point on any technology starts going down dollar for dollar the higher you go. In 2-3 years people will look at the i7 like they do now at the core2duo when in reality the core2duo is still capable.
It's how you determine to look at it. Personally I think i5 is the best bang for buck.