I doubt a nightly build would give you much - Toady is the only person working on the code, so it would only be updated at times Toady himself is actually adding code. Yes, that's often, but it's not all the time, even Toady takes a day off now and again. Then he does things like make ascii art for the donations or answer questions or stop to moderate the forums every now and again, and it's not like those are bad things, either.
Further, I doubt he actually just sticks every piece of code straight in the game. He has to work on functions individually, and probably creates very obvious bugs that crash the game or that do very obviously wrong things that Toady doesn't need to release to see have problems. The only things that would have immediate results are the bugfixes... and those are the things that he DOES release immediately, already.
In fact, this sudden update-haha-no-just-kidding-I'm-updating-it-again-whoops-too-late-update-it-some-more schedule is just making me nervous about trying to start up a serious fort I've been itching to start on the latest stable release, because I've not even made positively sure I like the site, and am reaching for the latest version of Legends Viewer to really scope out the world I'm going to build my fort on before SURPRISE! Your version is out of date again!