1) What other reasons are there to upgrade from poser 7 to poser pro?
You can call yourself a pro when using it? Seriously, besides the ones mentioned at SmithMicro, there aren't any others worth mentioning http://my.smithmicro.com/win/poserpro/index.html except for that everything seems to work a bit more smooth then with Poser 7 and Poser Pro uses less memory. If you do have a 64bit system and 64bit cpu (I guess you can't have one without the other) Poser Pro can finally use all of your memory for rendering, so you can do much more larger renders and render more complex scenes. The limit is now gone.

*2) Is the animation system in poser pro easier to use?
*It's as easy or as hard as always.

*3) Is there any documentation on how to perform a complex animation?
*Not sure, check http://www.poserpro.net/  it may (or may not) offer some help.

*4) Are there comparison screenshots of a poser 7 render vs poser pro render with its new features?
*I've seen some in the forums here, but you will have to dig them up or you can go here and find a few: http://www.runtimedna.com/mod/forum/messages.php?forum_id=95&ShowMessage=386634

*5) did they add global illumination?
*No.

If none of the new features excite you then skip this version and hope & pray that version 8 will be more to liking, if it will ever be released. I've side-graded from Poser 6 and it was worth it, but if I would have been a Poser 7 owner, I'm not sure if I would have upgraded for the price asked.

Artwork and 3DToons items, create the perfect place for you toon and other figures!

http://www.renderosity.com/mod/bcs/index.php?vendor=23722

Due to the childish TOS changes, I'm not allowed to link to my other products outside of Rendo anymore :(

Food for thought.....
https://www.youtube.com/watch?v=pYZw0dfLmLk