I got Poser 9 and have not really seen a big difference in regards to upgrading from Poser 8, I would upgrade to the higher one if you are planning on doing more in your poser, I don't do all that much other then render and a little rigging, most of my work is done in different programs that is why I got only the small upgrade, but if I had seen the difference I might not have upgraded at all.  Not that it is a bad program, just wanted to stay updated, and should have known better to go big or stay home.