Best of luck with your wife and family plans. As mentioned earlier, I wish for you that the harvesting of your wife eggs can be a suitable option to start a family.
As for the gift certificate, like many of the above posters, I don't think it would dishonor the intent of the gift at all if you used it for other PF necessities, like some Core books. Especially if you're DMing! As Mr Solis pointed out, it was a safe move to send a gift certificate for an unrealeased AP, for someone not knowing which products you own or not. Of course, the gift certificate could have been without a "for X product" mention, but that's probably just because the person being the gift believed you already had all the core you nneded, and also believed, probably with reason, that Kingmaker is going to be awesomeness incarnate...