How many pair of speakers do you own?

8 pairs. One pair of floorstanders, the rest are monitors. All are in use at various times.
Another pair on the way.

at last count 7...reason? for fun. listed by size:
JBL L-200
JBL L-166
AR 11
Epicure 10
Spica TC-50
Chario Academy 1
Ensemble Animata

To answer your second question, none of your suggested answers applies.

In my case, (1) when I upgrade, I don't get rid of the old equipment -- they usually just get reallocated to other rooms; and (2) I think it's nice to be able to listen to good music reproduction in different rooms especially when it is also consistent with the decor. Do you have children? Are they into music? Should they have their own stereos, too?

Of my 8 pairs + 1, 2 pairs + 1 center channel are in my main system, which is both my best stereo and home theater system, and 4 pairs are in stereo systems in other rooms. (2 pairs are in storage.)

1) 1 pair Cain Abby (main speakers)
2) 2 Mission 731i, 70C, Sony Surrounds ("Home theater")
3) Tivoli Model One
4) maybe a pair of Quad ELS57

Total 8-10 speakers sitting around.