I would go with a PSR1500 over a PSR2000..
More polyphony..96 to 64..

Better USB connection..
Better sounds..

It is an easy decision if you do not need a harmonizer.....but , bumping up to a PSR3000 makes more sense, if the money is not a factor...The 3k would be easier to resale than the PSR1500 or PSR 2000...and resale is important..it was important for me,,to get out of the PSR2100[I just don't like the PSR's...Good value[price wise]..but you really get what you paid for..