I think if you have the space to store stuff and you like the stuff you have, you should store it.
We had no closets in either of our houses but finally got a shed. I was much happier to have saved a few things for the new babe than to have to run out in my "nesting frenzy" and buy them all again.
I do wish I had kept the cloth diapers and my maternity pants and even a bunch of clothes.
I think it is a waste of money to give things away or even sell them for a reduced price if you know you are going to use them in the future.
I am finally getting rid of everything, even the swing. It is kind of a ceremonial "I'm not having any more kids" thing.