Thinking of upgrading...

#1 "much more advanced to use" ---> I'd say easier to use. The editors are a lot nicer, much more user friendly - but still pretty familiar. TorqueScript is still pretty much the same thing with a slightly different folder structure but it shouldn't take much working out if you know your way around TGE.

You might as well download the T3D demo and have a play about with it, see what you think, etc.

#2 I just did :)

I like the project manager and the new physics. I was looking into making destructable buildings for TGE. Also, the new graphical shaders and features such as constructing rivers are pretty neat.

Overall, Torque3D looks great, the only thing holding me back is the fact that I've already spent about a year on a game for TGE and upgrading may take time.

#3 That would depend on how much you've changed the source code in TGE. If you haven't made any changes then it should port over fairly easily. You just have to account for directory changes, some deprecated and new functions.

#4 Well I've implemented a few resources to TGE, such as render water under terrain, modernization kit (don't think I'll need it for Torque3D haha), Eric Hartman's grapple hook code and a few other things.

#5 I wouldn't advise switching engines mid-development - Duke Nukem Forever did that several times, and look at where it got them! When your current project is finished, that's the time to consider upgrading for your next one.