I finally did it, something I thought I'd never do: I bought a DLC.
So far, the thing doesn't seem like a mistake. All the games seem pretty solid (though I haven't played Superior Soldier because fighters and standard gamepads don't mix).
As for the whole collection, the only problems I've had thus far are:
1. The sound is a little scratchy (most noticable with R-Type Leo), though I've heard this depends on your soundcard.
2. If playing with an X-Box 360 controller, all the movement is done via the left analog stick, and there's no way to remap it to the D-Pad. For some games this is easy to get used to. Others, not so much.
All in all though, it seems like it was worth the $14.99. Here's hoping they do a Volume 2, if anything just to include the games they missed out on this time.