Well, the computer I currently have, I've had since August last year. Only thing I've changed, is video card and added 3 new hard drives. Computers last longer then what people think - it's just they don't stay "new" very long anymore.
The 3700+ would be much better then your current Intel. I prefer AMD over Intel always, but that's just me. I'm not sure on what kind of scores they would get, but the 2.8ghz p4 is fairly old now, being only on the northwood core (i believe...). The 3700+ would be a noticeable performance increase.
And weakness/vulnerability? There isn't that much difference anymore. Just die hard AMD fans, and diehard Intel fans. AMD used to have heat issues...not anymore. Intel used to be bad for gaming, but the Conroe has thrown that away as well.
It just goes down to cost and purpose now. I'm always going to prefer AMD over Intel for gaming. But that's how I've been taught in this world of computers that we live in
