A good, cheap test mule is a good way to try DD...I did the same thing on a JVC DD bought on ebay for $50 a couple years ago. Belt Drives, inasmuch as I appreciate their stone cold pitch black quiet passages, also drive me insane with their inability to hold a note perfectly stable (like CD); most notable on piano, string and other instruments that play in the upper registers.
You can't improve the speed/stability specs to 1200-series levels, but if you put it on a good support underneath, damp the hell out of the deck and platter, and get your cartridge aligned right in the new headshell.....you will at least get a quickie understanding of the performance of the better, more expensive, DD tables out there.
Most likely the SL-D2 is a lighter weight Technics deck....about 10 lbs of Plast-i-Clay inside the deck itself might be your best and most significant avenue to improve it's performance. $40 and a couple hours of your time applying it will likely pay off rich dividends
