At the moment we're keeping everything that DD grows out of and storing it in the loft.
I looked at the pile the other day putting Christmas decs away and thought, if I could make that decision, we could get rid of it all....
It's still there, and the cot will be kept too when I finally put DD in a bed, just in case.
I'm hoping time will sort it, either way:
A) as we move on with the 3 DC, I'll realise that I don't want to go back to the baby stage and do it all again (bizarrely things like Sing & Sign/playgroups/etc that I've done with all 3 really put me off a 4th!)
or
B) as they all grow and become less dependent he'll realise that one more wouldn't be so bad.
Sitting on the fence big time I know 
We have a big car already, we don't go on big holidays already (though maybe that would change as DD grows, and DS2 (who has SN) gets better at new things/places), we have the clothes/toys/stuff for a baby, very little would have to be bought. We don't have a spare room (we do at the mo but the boys share, if they wanted their own room then we wouldn't have a spare for the 4th for each to have their own room) but always talked about converting the loft.
We don't get much help from family as it is anyway, though PIL have looked after 3 for us, would they manage 4? and being older by then too?
I wish that I felt finished. I wish I wanted 3, had 3, and was now done. I would be getting rid of so much crap stuff and moving on with joy :)