All that content definitely slows down loading of the game, but I think once Trainz has what it needs for a route, it shouldn't need to look again. I have -keepallresources=1 in my trainzoptions which makes a difference jumping from surveyor to driver. I'm unimpressed with archiving. I kept the include dependencies checked and built-in content caused a flag. When I tried to install from archives, a lot of content was listed as new asset with a question mark. Another time though, I archived Clear Lake and moved it to a different computer and everything was there, all dependencies. I've got 23gb in my local folder and still haven't decided what's the best way. I'm leaning towards .cdps. While more labor intensive, I can better monitor remaining disk space and I'm sure exactly what's on a disk.
Norm