Upgrade because of the applications you're using.
I use FCP 7.03 and FCP Xi. To give you an idea of the difference, FCP Xi is built so that the more RAM present, the more it will use and the better it will cope with the edit. With FCP 7.03, it uses a finite amount of RAM (4 Gigs) so ta better graphics card, processor etc... will produce improvements. If I wanted to focus on FCP 7.03 I would upgrade my machine but with FCP Xi, I would simply upgrade the RAM.
My understanding of Adobe's products is it is a bit of both, but if it was my choice, I would upgrade the machine because the software will greatly benefit from the better processor etc...
"80% of success is turning up" - Woody Allen