I really comes down to th individual, if you think you have too much stuff then you should let something go, the A4000 abd A600(if its NTSC) will be very saught after in the US so you'll have no problem selling them.
You could check out Amibay
where there are people registered looking for these very items.
I have a pretty large selection of Amiga's and I'm using them all at least once a week, I've really enjoyed the project side of things and upgrading them so thats why I have so many now.
I certainly don't need anymore so its just a case of consolidating what I have now, with little mods here and there
All the best whatever you decide.