Personally I'd rather stick anything I'd already built, constructed, unlocked or paid for into the inventory to be sold / upgraded or used again as and when space is available.
It looks as though this will eventually be possible with the inventory tab and the E and B sub tabs .....see no reason why things couldn't be sold from the inventory directly ....that would save a lot of wrongly and quickly clicked things being accidentally sold or paths of production being disrupted, simply move the item firstly to the inventory and sell from there.