It seems extremely unlikely but I can't seem to figure another culprit at this time. I also noticed another person on the Nexus having an identical issue to myself who happened to have TTW installed. Basically everything in the MCM menu for Selective-Fire appears to be working, but in gameplay the select fire and all the other options of the mod do nothing.
I've tried numerous different saves with the same load order and nothing worked apart from a completely unmodded goodsprings save. Starting in the vault seems to keep it from working for me, though I have no idea why.
Edit: D'oh! I just didn't read the mod thread carefully enough to notice what was causing the problem. A user posted a fixed esp there already. Sorry for wasting anyone's time.