I was also thinking Donkey Kong 64. I can't think of a set location that I would set it at.
I'm thinking about a really long and high but not wide map with barrels bouncing (simulated through func_train).

I actually want to keep the lighting unless too many people are having to lower the gamma. Some can't raise it though, which is the problem. [...] If you know how to open up a pk3 replace- scripts/nintendo_land_b2.shader with this file and you'l be happy you did. B3 already has this but it will probably be a few more days before it comes out.
Whoever changes their local PK3 will get a new one from server because the checksum is different. You could as well make an extra release.
And about the gamma:
Well, I shouldn't rant about an outdated engine. But OMFG do I
HATE that the lightmaps have such ugly steps. Where in the calculation chain does that happen? There are still 256 possible brightness steps, but the lightmaps only have like 16 or something, at least in the darker parts. So, everyone has to make their maps bright. Hardly you see any dark and gloomy ones. Guess why.
I think it might be worth to try a map lightened for target gamma 1 (as in "unchanged"). I know that display devices (CRT, TFT, monitor, whateveryoucallit) have no linear gamma. They show everything too dark (except of course colors near no and full brightness), and a graphics engine that creates graphics for a true linear gamma is hardly wrong in doing so. But somewhere in the chain of algorithms, something is wrong.
And to fix that, maybe it's worth a try to teleport the whole Tremulous world to a target gamma of 1 (meaning: the "too dark" display that the Desktop and the Web have) to have more dark color steps in the lightmaps. The model textures would have to be changed, though.
That again could all be done client-side and with a key in worldspawn. Like "thisisanewgammamap" or something. The clients could then adjust the model textures and the display gamma.
By the way: There belongs a gamma key into the worldspawn anyway. That could solve the whole "I have to adjust my gamma for this map" issue.