Just some personal remarks :

The SD1 is much heavier than e.g. the Tyros because of the 'semi-weighted' keys. Every single key has a metal part in it. This creates the great keyboard'feel'.

Tommy :
Almost all displays cause the problems you described, sooner or later. My SD1 display was replaced for free.... no questions about the SD1 age! (2.5 years)

It is mentioned by others already : Speed up the processor, harddisk and the FDD.

Perhaps the switches/buttons need some improvement in size/color/quality/feel ?

An internal sequencer is not required.
Built in speakers not required.
CD-ROM /burner not required

Having a clock in the display would be nice (like WX'es have)
Stereo sampler & vocalizer are both a must.

Roel