Off topic...
Yeah, I used to map for DoD 1.3 and it was great fun, not all that much different from mapping for HL or CS, but it seemed more realistic to me. I liked the end result, textures and models... the goal system was easier that TFC.
On Topic.
Spirit is a brilliant modification option. It is relatively easy to use and adds functionality.
It hasn't been taken up by most of the community.
A reason for that might be that most people new to mapping feel that Spirit will solve all their problems, when the reality is that it creates more if you don't understand the basics.
As for downloading it... Not really, most people who release a Spirit based Mod include the dll in the download, so the player doesn't actually need Spirit.
There were a lot of members here at TWHL that tried to map with Spirit but I haven't seen anything come of it... Although one of the recent compo entries used Spirit.
Some people love it... Some hate it.
I think it is worth trying, if only to look at the test maps.