Cool boards! For the Core+SID, maybe check a few clearances:
bottom left mounting hole + J5 header (header may be more convenient as a 2*5, or even 2* 2*5 as is done in the Core8. But I see there's not much space)
LCD and CAN headers
trimmer pot on the left might be too close to the board edge, normally they don't like holes/plating near to the the milling cutter. (Shouldn't there be two pots, one for brightness and one for contrast?)
I would put the voltage regulators at the edge of the board, this way they're easier to heatsink if needed and they radiate heat away from the SIDs/capacitors etc.
Is there a reason for two bridge rectifiers?
Have you thought about the grounding scheme around the SIDs? I know the MB-6582 board has a gap in the ground plane, presumably to keep the digital noise off the audio circuits.
You can check the sammichSID layout for inspiration, although it's a little bigger than your 10*10cm.