they tell me that they have all they need.
Ok course, why spend money on games when you can use demos? You have less chances of having installer problems, as the demo installer isn't usually as advanced as the retail one, and most of the functionality needed by the game is in the demo anyway.
That suggests saving it for this purpose would be prudent.
Save it until we have a good reason to sped it. That reason could be wineconf, or something else, in the mean time keep it in the bank.
Ivan.