@Funk_Illuminati have a look through this thread
I don’t have any experience with the Moog Song Producer other than seeing it online a few times, IIRC around 10-15 years ago a number of new old stock ones appeared for sale on eBay US and appeared on Matrixsynth blog. It always looked interesting, although I don’t know how useful it would be today.
There is quite a thriving scene for C64 stuff, with lots of new peripherals and software still being made today, including quite a few music making tools and hardware.
The C64 itself is a pretty capable synth, given its age and with some caveats, but if you are determined to get a C64 setup working IMHO it is well worth it. Although obviously it is associated with chiptune, it is also capable of a wider range of sounds than typical chiptune stuff. It has a really nice PWM, some people say it is their favourite PWM sound.
I don’t use my C64 setup all the time, but it is great to have there when I feel like using it, I use mainly Mssiah, Cynthcart, Defmon, Midislave and a few other programs.
If you want to use it with midi Mssiah and Kerberos are both excellent and work well.