It originated as a high performance home machine that proved to be rugged enough for DJ use. However, most enhancements to the Sl12x0 series after MkII were for DJ use. The M5G model (Grandmaster) has an enhancement that is of particular use to audiophiles--OFC tonearm wire. Plus it comes with a screw-in headshell weight and a screw-on tonearm stub weight, expanding the range of cartridges that can be mounted and balanced on it.
Aftermarket enhancements are available from KABUSA.com
stateside and Sound Hi Fi
in the UK.
The Technics SL12x0 series is the industry standard for that type of turntable. However, the best poor man's knockoff is probably the Audio Technica PL-120, with a list price near $400 but available online for a little over $200.