Selective games category [Suggestion]

You mean like wishlist? :)

I think a recommandation list based on the tags of the games in your library could be nice. That's a part of the recommandation list that steam store generates.

Your recommendations list should automatically update to include games you've entered giveaways for.
There's no way to avoid having to hide games if your primary source of new games is SG, or avoiding using Wishlist if your primary source of new games is Steam. Thanks to Valve's "Any trashware welcome!" policy, the core list of giveaways available on SG is always going to be massive in variety, and thus will require that level of attention through one front or another. Past that, what you're asking for seems to already be in place, assuming you're entering giveaways selectively enough that you're not flooding out your recommendations list with random giveaways.

Rather, what you seem to be asking for is a secondary wishlist- which, honestly, comes across more like you're trying to bypass filters that restrict wishlists to a certain count than anything else; As, after all, why would you take the time to establish an elaborate second wishlist in the first place, if they're not games you feel warrant inclusion in your main wishlist?
Perhaps if you elaborated your perspective more, we could have a clearer idea of what options may be available. In the meantime, Recommendations should already function enough like a second wishlist to meet any requirements you may have, regardless of what perspective they may be based in.

In any case, cg doesn't attend to things with core relevance to the site, so expecting him to implement something that seems to be exclusively niche to your personal usage isn't something that much hope should be put into.

So...um why not just increase your wishlist?