Sadly a bog-standard A2000 won't give you a lot of money. I picked one up for 20 Euros a few weeks ago and that is a machine with 68020, SCSI, extra RAM, Amiga internal Genlock and some harddrives, as well as an 8088 bridgeboard. My advise: If you've got the room, keep it! Make sure the battery won't leak and use it as a onrament for the house, play with it on the first cold day of the year.
The 1200 and the Blizzard should keep you busy for some time to come :-). If the 1200 came with Workbench 3.0 (it should have!) you can check the version of your ROM with Showconfig. It should help you determine if you've got the 3.0 or 3.1 ROMs. If you've got the latter there's no need to buy them.
From what I know 3,9 is especially handy if you're having a PPC and a grafix card. Correct me if I'm wrong but I guess 3.5 should be good enough for the 1200 you own.