Keeping two versions may solve the short term problem, but over the long term it's definately not the ideal solution.  The problem is only going to get worse the longer you hang onto the older version.  Eventually you'll be passed by by people utilizing the better software and it's new features.  Also, exporting to release 14 or 2000 formats probably isn't going to work for 3d models.  It's been my experience so far when saving back that elements that can't be created in the version you're saving back to either get mangled or deleted.  I can do some testing when we get upgraded to 2007 and see what happens.  I've also noticed that having two versions on a system tends to screw things up, I'm not sure why, I just know that when we had 2002 and 2005 on our systems at the same time it was creating bugs and errors and corrupting files.

Ryan, Oh don't I know it, Bently and Autodesk are insanely proprietary and it's always user error when something goes wrong or doesn't work, the software really can do no wrong according to them.  Around here if something funky happens we just call it a "feature" of the program.  That's all that really happens when you upgrade, they fix the "features" from the last version, change the format just enough so people have to upgrade, and add new bugs...oops...sorry..."features" for the user to worry about.

It's funny because as Microstation advances it's taking on more of Autocad's features, and as Autocad advances it's taking on more of Microstation's features (in program rendering advances and eliminating export options being the ones that affect us the most) pretty soon you'll have AutoStation and MicroCAD :)

One thing I noticed, the polytrans people said that the reason Autocad is dropping the 3ds format is because it's an old out of date DOS format, which I could understand if it wasn't for the fact that Autodesk told our support people that the best way to export files from Autocad was to take them into 3d Studio Max and then export them from there as .3ds.  If they were eliminating the format because it's old then why is it still in 3d Studio Max???

At this point I'm recommending the Lighwave/Xstream/Vue 5 package as our standard, as it seems to be the cheapest and more efficient way as well as getting away from the whole "Autodesk rules the world" complex that you'd have to deal with using 3d Studio or Maya.  I've seen some really good work utilizing this and am finding a few people who are already using this workflow.  It definately sucks that we even have to deal with this stuff, as I too had developed a really nice workflow from Autocad (which I know really really well and can work really fast in) and Vue.  It would be nice if things didn't change but I've discovered the 3d world changes extremely fast and you have to be aggressive  and proactive in order to keep up with it.