To upgrage CPU or just wait it out?

I have a dell inspiron 700m and love it. Boots in about a minute and I am pretty happy with its overall performance for its size. But being a student I find myself using more and more powerful programs. I often use photoshop, illustrator, sketchup, autocad, and sometimes all at the same time. I have 2GB of ram installed and the 725 1.6GHz CPU. The only problem I have is that my CPU is usually pinned at 100% anytime I orbit around objects in sketchup or anything out of the norm in photoshop. Basically anything graphics heavy even visualizer in iTunes. I'm just wondering if it would be worth it to purchase the 755 2.0GHz used for about 85 on ebay? Or should I just hold on for awhile till this summer when I get a new mac?