I have imported content from TS2004 into TS2012. Depending on how complicated the content is, you might have to do a lot of error-correcting, but it is possible to gather up items from previous Trainz versions. Routes themselves may be a bit more problematic as the structure of the files changed between 2006 and 2009 (at least I think it was those two versions) and it is quite possible you would get a "blue sky" route (which menas all you see is blue sky and nothing else).
having said that, a lot of content for older versions looks bad on newer versions of Trainz.
Bill