Now you can see what the upgrade will be once you have collected all cards of that type you need in order to buy the upgrade. Is there an in-game way to see what the upgrade will be, so you can choose which type of cards to request / keep?
I know you can check the Clash Royale Wikia, but in-game would save browsing, searching and checking your current level.
Yes you can. It’s qutie simple actually:
An upgrade adds +10% to the stats.
For troops: +10% Hit-points +10% Damage +10% Damage per Second For Buildings its: +10% Hit-points +1 Troop level/ +10% Damage For Spells its: +10% Damage (for freeze +0.3s duration)