We can't answer if it's worth it. That depends on how much extra cash you have, how much background rendering you could take advantage of, how much value you place on your time saved, and a host of other things. It's like asking if it is worth upgrading from a Nikon D90 to a D300 - the image quality is nearly identical, but the extra features and speed of the D300 add to the cost. Both take great pictures, but the D300 focuses faster, shoots faster, has more options, and supports more things in the context of a larger workflow.

The same is true of Poser Pro 2010 versus Poser 8. The image quality is nearly identical, but you'll have to do extra work (sometimes a LOT of extra work) to get the same outcome in P8 as you'd get in PP2010. It also depends on your hardware as to whether or not PP2010 is actually going to save you time rendering.

As for the differences, look here:

http://poser.smithmicro.com/comparison.html

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)