When I played xcom last weekend, I had a moment where my storages were full at some point.
What I wanted to do is to sell items until I had again a little bit of space, but I had to sell something, switch back to base information to check how it affected the storage space, back to sell, back to base info, etc...
So information about the storage space on both sell and buy screens would be nice too, since there is a little space to the right of those buttons, you can only make use of the precious screen space