Spartan3 decoupling

Hi, I'm making a board with a Spartan3 XC3S200, half of its pins available as I/O are yet occupied and I'd like to bring all the others so far unused to a common connector in order to have them ready for future use. I'm now working with xapp623 (PDS) to select the decoupling capacitors. My question is, as far as I don't know if I'll use the free I/O as input or output, could I place one decoupling capacitor for each Vcco-GND pair? I mean, placing more decoupling that what you really need is only a waste of space or is a completely wrong approach? I suppose that more capacitors is better than less, i.e. I do not have to place less decoupling that what suggested in xapp623, but I can decide to do more than that. Thanks, Marco