How about the attic? Can you access it? Or do you have a flat roof?
Having a shed is convenient, but also convenient to thieves. It can get tough living in a city.
If you must have N+1, you can rent a storage garage for those not often ridden collectibles. But you'd have to venture outside metro Boston to find good rates. I got a quote of $35/month for a half-garage in NH, when I was still living in Boston.

I went from a 2 bedroom condo in Brighton to a 3-car garage, 2800+ sq ft house, I thought I had enough space. But that proved to be wrong very quickly. Currently there are 10 full bikes in there, 2 my wife's, 1 my son's, and the rest are mine. 4-5 flips in various stages, and boxed frames (~9 all projects in need of work) !!!
I have too much crap!
So, it's probably more of a mixed blessing that you are short of space. The additions are sidetracking me from riding. :-\