The older templates are just as stable with security features as well?
I would say yes. Usually when a security vulnerability is posted for Joomla, if it's template specific, any templates based on that bit of code are checked and corrected. Some people choose the older templates as there is less dynamic code involved to offer up a security issue.
There is less activity on the forum from members for the older templates mostly because people usually want the newest thing with the newest features, but we support all of them and check all forums regularly to provide assistance.
The only other thing to consider is if you're moving to Joomla 1.6. Migrating templates over to Joomla 1.6 is a real time consuming thing, so a template from 2008 might not make it to the move...at least not anytime soon. But many of us are sticking with Joomla 1.5 for a good long while so it will be fine to use there.