yes, spend it all every run. I usually just buy land (forests, so I can delay setting up foresters a bit longer), because early techs are easy enough to research anyway, and late game techs are too expensive to buy with HP xD
It seems mostly finished. It looks like the author got it to a point where it can be considered a 'finished game', and moved on.
I guess officially it is a version 1.3.10, and probably version 1.0 is what the author considered to be the 'full game', with updates 1.1, 1.2, and 1.3 adding some extra content, reworking some existing features etc., and some other minor updates being mostly bugfixes and such. But as you can see there hasn't been much going on for a few years, so I wouldn't expect new content at this point.
As for the wiki, well... it's a small game with a very tiny playerbase. Probably some player at some point created the wiki, the author probably linked it in the game because it was the best documentation for the game available, even if incomplete... but then probably the original wiki author lost interest. In the end, wikis are meant to be a community effort, where anyone can fill in missing information. For big games with a big community it works, there's always people willing to update the wiki. For a tiny game like this, not so much.