There is something to be said for keeping the clutter to a minimum. It's something I struggle with.
You can try asking yourself these questions:
Do I love it? (usually yes for me)
Can I afford it?
What will I do with it? ( I do try to have a purpose for my machines)
Where will I put it? (This is a tough one. I'm about out of room.)
If the answers are favorable go ahead and get it.
If storage is becoming an issue you can always rehome the ones you're not in love with. Fix them and sell them to someone who will be happy to have them. That way you know the machines are being cared for and you can still enjoy finding machines while improving your collection at the same time.
One thing I've started to do is have a machine or two available to give to kids who want to sew. Given the fact that many schools no longer have home-ec type classes where sewing is taught and many children's parents don't know how to sew either it falls to people like us to teach the ones who want to learn.
Rodney