It would be worth it if you do the following, buy the 3000+ now then the X2 5000+ next year.
I know in Canada the X2 3800+ is about $450 CDN and the 3000+ is about $200 CDN.
So, if someone bought a 3000+ for $200 CDN then spent $200 CDN next year on that same dual core, then they'd still spend a total of $400 CDN. Of course, they could still sell the 3000+ on eBay but by then it would be worth like $50 CDN on eBay. So, total cost $350 CDN when they could get the X2 right now for an extra $100 CDN and have it for a full year more.
On the other hand, you'd save money by getting let's say an X2 4600+ next year. My impression is AMD will take their time to lower the price on the X2 4800+ and especially the X2 5000+ when it comes out. They're snobs in that way. The same thing happens for top of the line video cards. They don't want to give away their top of the line (always a stupid premium).