Dragon Valley never gets full sun and it drives me nuts. Everything looks like it's taking place at twilight. Is it meant to be that dark all the time? If not, what can I do to fix it? Actually if so, are there mods to fix it?

Hm, a screenshot might be helpful here.

This is as bright as it gets during full sun. It's noticeably darker than any other town I run, even Monte Vista. It's all...dun and dim every time I play in it.

(it's a Final Fantasy VI house btw)

Yes, this looks like the normal DV lighting. It's quite warm and mellow. Personally I wouldn't call it "really dark", however. So, the only thing you can do is to use a lighting mod, and I guess you'll need one that also changes light angle. I think that part of what you feel as being too dark is also due to how light in DV comes from a much "lower" angle compared to other worlds.

Here's a comparison picture from my game. Default light, summer season:

Yeah, that looks like it's evening to me. But at least I know it's not just my game. Thanks!

If you're looking for a lighting mod that makes things brighter, I definitely recommend these by brntwaffles:

Blue Skies & Sunshine
Frozen inspired lighting mod (this one also has stronger colors)
Dragon Valley lighting adjustment