Telika: I don't. I also now own a big part og the GOG library, and I'm used to see discounts or awesome opportunities on games I already own. I didn't expect the gift randomizer to function differently from, say, the randomness or GOG's discount choices during normal weekdays.
I really experience it like I experience the regular evryday discounts, and am not expecting more. Anyway, what if a GOGer has all the games, or all the games but two or three ? Would the same games be offered everyday in his gift packs ?
While I completely agree with you, as I too am used to deals in games I own being the norm, it's also true that I will spend more $ in GOG if I get Costume quest for 3$ on my surprise box (a game that I not only don't own, but is also on my wishlist) than if I get Omerta, a game I not only alrdeady own but it also happens to be on the 80% discount for that day.
So, while I don't feel particularly disappointed for not getting games I'm interested in on the surprise box, or even games I already own; I do see why it might be worth it to personalize that randomness. But hey, it's not my problem, I'm in no hurry to play costume quest.