I bought my cheap SE for MIDI use months ago. I do have a lot of obscure software and barely figured out what will run on it.
So far I have been able to run:
Logic 1.7 - found the software somewhere shady, but I happened to have a working dongle for it.
Alchemy - audio editor, don't remember version, does sampler import & export too
Softsynth68k - IIRC, older version of TurboSynth
M v0.96 - fun algorithmic jamming
Jam Factory - "
Max v2.5.1 - all-purpose MIDI patchable toolbox
MCL 2.x - LISP IDE, has some MIDI bits
Music Mouse - Laurie Spiegel's gestural interface
I did score various versions of Performer and Vision, but yet to figure out which versions will run. One issue I have experienced is that my SE has two 800k disk drives, some programs on 1.4M disks might work but I can't properly use images of them. I also have an SE/30 but it has SCSI issues for now. The stock SE handled a bit slow with regards to draw routines which would not bother me for a sequencer but is not so good for performance apps. Mine now runs an 030 upgrade and doesn't draw with a lag anymore. Main thing which keeps me from using it regularly is my very very loud external hard drive. It is even much louder than my MDD "wind tunnel" G4... Hoping to upgrade it to a solid state disk sometime.