I still haven't picked up my A4000, but I was wondering - is it worth using a scandoubler in one...as I was under the impression that the AGA can scan double to an extent?
I cannot say that AGA scandoubles. I tried using a vga-monitor on my A4k for a while and that really didn't make me any happier than the 1084. You have that odd screenmode that looks quite well without a scandoubler but that screenmode is sooooo slow that you don't want to use it. Using a scandoubler makes things a lot easier but you still need a flickerfixer as well. So, I would recommend that you get a gfx-card like a Cybervision 64 or 64/3D, a Picasso II or IV. I dont think its that impossible to get a used one for a decent price. Considering the difference I think it's worth the extra money and the difference in price from a scandoubler/flickerfixer up to a gfx-card is definately not that much.
The only Amiga to my knowledge that doesn't need extra hardware to work well on a modern monitor is an A3000 that has a built-in flickerfixer, no AGA-machine has that.