No one ever went broke taking profit! As CarnivalBigTop would say: sick gainz bro.
I don't speculate/trade cards much, but I did pick up 3 priestesses the second I saw the first MJ preview. I then sold the 3rd one for more than all 3 cost me once everyone caught on. I could have bought more and gambled, but I don't feel like stressing over my video games.
The only card I question selling is Untold Greed. I don't know how much it cost you, but it's a great card for any aggro death deck. I run it in zombies and anubians. Zombies are pretty locked in, so at least some of the value proposition of that card is fixed.
Stoneskin is a really solid card. I hope that pays off for you. If the game hits even 100k players, you're gonna be sitting pretty. Best of luck on that trade plan :)
I could have bought more -
I wanted too but I wasn't confident about my ability to foresee GU prices.
Untold Greed - I bought it late and expensive:
But I got some noticeable profit in USD - because ETH was low when I bought it, 30% cheaper than today.
The card is amazing and I feel unhappy to say goodbye to it. But Necronomics is also great and it costs 3 times less than Untold Greed. This is what Untold Greed might cost in case Anubians are nerfed. I will buy 2 if it happens.
Anyway, I have no time for GU experiments and even grinding these days. I have shiny Deception - this is enough for me.
If the game hits even 100k players -
It might happen if they have a generous P&E program.
I believe some people hoard cards like Stoneskin so, sooner or later, they will rule the supply, not random people who need 0.2$ asap. Stoneskin might become much pricier even without reaching a 100k player base. Maybe.