With the same cart/stylus, do the GT 750 and 2000 sound different? If so, how?
The design philosophy of higher end turntables is to make them as transparent as possible so that the difference you would hear between a GT 750 and a higher end table is silence. And actually, at this level of performance, a normal human wouldn't be able to hear the difference between a 80db table and a 85db table (perhaps between a 80db and a 95db table, but I don't have a 95db table). What you pay for, at this level, are measurable improvements in specs (that can be consistently measured by third parties) and the assurance that when you listen to a bad recording, that it's actually issues with the recording and not your high performance table (of course, it could be your cartridge).
Superior specs cost money and you can see what areas of design were found to be most important. It seems to be high processing power for speed accuracy (remember 1983 is when 32 bit processing was still two year away), computer balanced heavy platters (the more perfectly balanced the higher the cost and brass cost more than aluminum) and high precision bearings(or magnetic bearings in the case of Victor). Heavy plinth design added less to this equation and you can see this in the Pioneer PL3 vs the PL3a. They have identical plinth but the specs of the PL3a are colossal where as the PL3 is still stuck in the 70s.
So to answer the question posed by this thread, the plinth "cheapness" doesn't matter since it does the job. Replacing the plinth of a precision instrument will probably do more harm than good. There are much better turntables out there and of those, the GT 2000, seems to be very plentiful (at least in Japan). A Kenwood KP 990/9010/1100, would be a better table than a GT 750 but not as good as a GT 2000. If you want the ultimate table, my vote goes to the Pioneer PL3a with the Technics SL-1000mk3D in second place.
Of course, there is a caveat, the electronics of these great tables won't last forever and eventually there won't be any functioning units (at least until the price of rapid prototyping ic comes down to respectable levels and we can come up with the schematics of the problem ic).