I have the XD3 (no HD no Harm)
Is the SD3 worth upgrading to?

Don't know how much the XD3 would still give me, around 1,000 i assume?

Is the SD3 worth buying being that it's over $2,000 US ? Is it that much better

I remember playing th SD5 (keyboard version), it was very similar to my XD3, not a huge difference.

anyone?

Well,
the SD3 is exactly like the SD5, only without keyboard and speakers, so I guess that you have the answer already...

KETRON XD3 vs SD3

SOUNDS:- Most of the sounds of the SD3 are new and in some cases even better than the sounds of the flagship SD1Plus (such as guitars, violin, piano, strings, sax). More realism has been added especially to guitars which now have fret noise, strumming … etc. When used with the styles, they are even more realistic than before.
STYLES:- The new styles take use of the new voices. You now have a lot of bass slides and guitar strums and noises within a style making them more realistic. Most styles are now 16 or (as in the case of some RIFFs) 32 measures long making them less redundant and more realistic.
FEATURES:- A lot of new features have been included with the SD2 making music performance and creation more fun such as
Multi-tab buttons. Can be assigned to various functions OR used to call up registrations (whose names can now be displayed at the center of the screen).
Fill to Arranger. A user can now press any of the Arrangement tabs, and the SD3 will automatically insert a fill before going to the next arrangement.
RIFF. Unit now plays back complex chord progressions based on the style selected and the style of play.
After Fill. This feature allows you to trigger the Fill in by pressing harder on the keys – frees your hand so you focus on playing.
Hard Drive upgradeable. Upgrade HD to 80GB
MIDIJAY LINK – Control the Midijay functions directly via Midi from the SD2. Use the Midijay to increase library with Grooves, drum loops, audio (wave and Mp3 files) … etc