Thanks for your encouragement!
Reg the "Replay" card, there are no effects to indicate when the next card is played twice. But the effects should be visible in cards such as "Advance" (the tank will move forward two spaces if possible), or "Turn Right" (the tank will turn right twice, i.e. 180 degrees). For armour, double the amount of armour is gained. For attacks, again, there is only a single shell that is fired, but the damage is doubled. The one case where it doesn't have an effect is when you use a "Dynamic Shell/Armour" (I'll probably change that as well.)
Agreed that many a time, it is hard to find the card you want. Three are a few mechanics that increase the card selection power (a Mechanism that draws an extra card each turn, cards that draw more cards when played, etc.) But yes, this needs more work.
Appreciate the detailed feedback.