I've been thinking there needs to be a way, in the game itself, to manage multiple decks at the same time. You have a pool of cards, so a deck is just a set of pointers to the pool of cards - right? Why not have multiple, with one designated as "active" for use in any games? Only the "active" deck would need to meet the 30 card minimum, so the extras could be empty. If you put a card in your deck, it should still be in your pool - if you try to put the same card in one deck, it shouldn't work, but if you try to put the same card in multiple decks it should work.
I figure this way you can have a grinding deck, a no-upgrade pvp deck, an upgrade pvp deck, and a tinkering deck. So four decks would be about right. Newbies would start out with one default deck marked active, and they can start building new decks in the other 3 slots without losing the initial deck (think of that as a kid's comfort blanket). Then, when they get more cards, maybe they build SG's grinder rainbow - great agains level 5 and false gods, but not so great against real players.
Finally, they start building PvP decks. Want to grind? set grinder as active. Want to PvP? set something else as active. No time wasted setting up the deck from scratch. No having to remember what cards you wanted to put in or keeping written records of your decks. Oh... and might be handy to let people name their decks and show the deck name in the game.
Some issues to resolve - what happens when you upgrade a card that is in a deck? Do you remove it from the deck? What if htis lowers an active deck below 30 cards? Should be easy to figure out a solution to that.