Depends on what you plan to do and what you hope to accomplish with your computer or to keep it going at a certain pace for what you use it for.
In the long run a very high end system that lasts 3 years costs a lot less than a system that goes through 3 major upgrades over a 3 year period.
I did the math. It works out for me but it won't for a casual person.
In fact I save just enough to get a phase change within that 3 year period, which will extend the CPU's usefulness by almost a year or a year at most and the phase change can be reused from that point on for little cost, and you get to have top performance for a very long time as opposed to playing with a mid ranged system for 3 years straight. Which again saves me enough to get my LCD.
Can't wait. =)