I like the reasoning of a full booth, as a better place to talk and discuss. At a crowed place I personally would much rather go into a space for a bit of one on one talking than be pushed on down the aisle by the crowd.
but
Since it IS always hit and miss and you never know who will be interested in your product on that particular day and who won't be, saving half the money might be a wise thing in case it is a slower day. It might make a difference in whether you are able to financially do the NEXT show or not have the money for it.

I am the queen of wishy-washy answers