I set up a Jenkins server that automatically creates win32 builds from Quakespasm SVN:
http://quakespasm.ericwa.com/job/quakespasm/
Assuming this works, it should be the best way to help test QS development. Jenkins should automatically do a new build whenever someone commits a change in SVN (within an hour). There's even an RSS feed that should notify you when a new build is available.
The current build there, r935, has things like bsp2, non-power-of-two textures, part of mh's dynamic light speedup, shifting messages when the crosshair is present, new default keybindings in quakespasm.pak (WASD, mousewheel weapon switching, mouselook on).
Note that I have some patches which haven't been accepted into quakespasm SVN; for example, SDL2 support, improved audio resampler, some loading and rendering speedups. These aren't in the above build, but I'm planning to set up another project in Jenkins to build with these not-yet-accepted patches so you can test them too, if you're interested.
Also, making this produce OS X builds is on my todo list.