Runtimes can be linked between Poser versions and external, no need to move anything if you have the proper folder.

Generation 2?  Are you referring to Simon, Jessie, etc?  The only one that has gotten major attention is Miki.  For you, it would be Miki3 working with Poser 8.  There is not too much investment going on with these models but many users go back to them every so often.

V4 is still marketable because the conversion to the Genesis models has not caught on with the majority of Poser users.  I am revisiting this subject, but haven't formed an opinion yet.  It does have potentials.  However, there is an effort try to promote the current Poser legacy models (i.e., Roxie, Rex); many content can be found freely on the net.

If your intention is to upgrade soon, concentrate on the weightmapped models which have better bending and movement.  If you are interested in creating content and rigging, the PoserPro series will be more to your liking.