A600 is pretty much same speed as A1000, only slightly faster due to ECS chipset. A600 also some more memory by default than A1000.
Plain A600 surely isn't worth it, better keep the A1000.
If you need an expandable Amiga, get A1200. A1200 has the best set of expansions available, while still being reasonably priced. If you're loaded with cash, you could think about A4000...
Amiga History Guide The 'Classic Amiga' Range
