Well, I worked a little on it. And although I didn't improve the actual smps playback a lot (aside from a few small bugfixes), I made a lot of other changes.
At first, it can log v1.60 VGMs. (press V to enable/disable logging)
Also all DACs sounds and PSG envelopes are dynamically loaded and are easy to change. (I included a small editor for the PSG envelope files.)
And I removed Allegro (and made it a console app), so it continues playing if the program doesn't have the focus.
Finally, there is a 32-bit version (compiled with MSVC6 for compatibility) and a 64-bit versions (compiled with MSVC2010, so you need .NET 4.0).
EDIT: File updated, see this post