I still release '04 / '06 items from time to time, but the majority of my work is in TS2010 now (back-reved to '09). The new bridges and track all use new features in '09 also, to make them more efficient. Converting the bridges back to an earlier version should be possible without changing the GMAX. The normal mapping may cause issues in old versions, though, but I'm not sure.
Ben Neal has several standard and narrow gauged old west locomotives on his site (http://steammachine.com/bdaneal/
); all his are for '04 / 06. Terry Bryson has some Civil War locos on the DLS, and Elvenor has a number of narrow gauge old west equipment on the DLS.