Just do like me and keep'em all!
I got back into this hobby several years ago when I found a A4000 for sale cheap locally and figured that it was most evolved Amiga and one that I could never afford so I picked it up for just a nostalgic romp.
That was 7 1000's, 8 2000's, 5 3000's and 4 4000's ago not to mention a room full of hardware and let's not even get started on the 8-bit stuff!

I got the room so I figured why not. Now if I can ever get the time to actually use them instead of fix/restore them.
Short answer...... keep both.