This topic comes up occasionally, and unfortunately you'll find there's really no clear answer. I spent a few years slowly decking out my A2000 with '060, PIV, etc. It was an immensely fun project, it's amazingly fast for what it is, and in some ways, it's my favorite computer ever.
On the other hand, I found I really did need AGA for demos, so I set the 1200 back up on the desk next to the 2000.
Then, you start wanting AGA and RTG on the same machine, but you can't let go of the other ones.
And so forth.
