Is a new MacBook Pro worth it when previous generations are selling for much less.

In a word, Yes. Check out this cpu shootout at barefeats.com. That plus the improved fit and finish, 50% fewer parts to fail and a graphics chip that should really shine when snow leopard ships next year+ the ability to address 6 MB of RAM. On the other hand, previous generation MBP's can be found for significanlty less and are still some of the best laptops on the planet.