It is absolutely worth it. I have several versions of Poser installed on my computer (back to Poser 8) and they all work, but I never use anything but Poser 11 unless I need to test something in an older version.

I love Poser 11 and think it's one of the best versions SM has ever put on the market. Of course, I do a lot of rigging and the rigging enhancements alone make it worth it for me.