Nice collection, always wanted an A4000, couldn't afford it then and cant now either
I think keeping the A4000 as a spare parts machine is pretty good justification. I keep an old a1200 mobo, a few floppy drives and various salvaged components around as a kind of emergency crash cart if my miggy dies.
Then again if you think it's getting too big they would have a happy home here
to actually answer your question I just have the 1 a1200 and it gets used on a daily basis, ether pro-tracker, games or me just tweaking the settings. I'm currently trying to see how modern I can make my Workbench look with the standard hardware. Personally I don't think I could ever sell the miggy and if I did I would probably get dragged back to ebay by nostalgia in a few months - Amiga is a bug and we've all been bitten, this is the curse we carry