Do you think card prices are going to go back up?

I believe they will go back up in time assuming the majority of the exploited gems are flushed from the system. Unless you absolutely need the steam wallet I would hold off on selling anything to see what happens, as of now there's no way they are going to fall any further.

Also if there is a craft event that yields items for event cards crafted then a heavy bulk of cards will be gone anyway.
Personally I'm just gonna craft mine and hold off on selling the ones I don't have a full set for until after the new year.

Unless they do a rollback, they will take quite a while to reset in prices.

The gems seem like a good idea though. They should theoretically create a bottom price for cards while also lowering some of the higher priced ones with the packs. Unless I misread the FAQ, I believe the Steam Gems will be staying after the event which should continue to maintain the bottom price for cards.

I don't think so, you can only craft 5 badges so if most people who want one get it really cheap now there will be no demand later...

No.

Cards are getting less desirable over time. Either because players don't need them anymore (crafted the badges already) or because the offer surpasses de demand by a lot.
Plus, people are getting tired of badges, they're learning that spending on these "money grabbing" useless items is idiotic so that leads to even more cards on the market.

Cards are only "monetary valuable" in games with very, very few players.

What do you mean card prices tanked? I took a quick look at my inventory and the cards are still selling at the price of around $0.45-$0.50 per set