(needed to add a tl;dr) - you have limited resources, spend it on moving forward.
Even though my music Mac is on 10.6.8, I think I’d rather see a one-man shop spend time moving forward and continuing to develop/fix/polish what’s there. Opening up the backwards-compatibility can of worms might be something to do if you had more resources helping you maintain the codebase.
I lug my OTs up to the Windows PC for OctaEdit interaction when needed. Yeah, it’s a slight hassle, but not bad. Even though I deal with computers and programming all day long, I’m very reluctant to upgrade that music machine since it’s got stuff like Tracktion 3.0 and drivers/apps for my Weiss AFI-1 AES->Firewire converter and other crap like that. Researching drivers, pulling down updates, etc is not something I’m comfortable with in the Mac world, so I leave that machine alone.
The real answer is to learn about Time Machine, buy an SSD and copy the drive and swap in the SSD and upgrade and see what happens, but I just don’t have the heart to start that whole thing right now.