Only very vaguely guilty, and that's more due to what I planned to spend it on. I'd feel less comfortable spending it on whatever, but feel better having decided to buy a buggy with it. It will stop me spending silly amounts of money (as I won't spend more than the grant) and help keep me healthy as I'll need to do lots of walking with it after the birth to lose the baby weight. But if you really don't need it, donating it to a good cause seems like a great idea.
Don't be silly. I presume you have been paying tax for most of your working life? If so then this grant is your entitlement (for now, until it gets cut alongside all the other things that are going to get sliced post election). If you are very wealthy, presumably you already make charitable donations to appropriate causes?