Combining my idea with those, you could have the suits set up as overarching offense/defense/utility/summons categories as I suggested and then give each number or face card a specific theme: 3 might be fooling sight (blindness/deafness for offense, mirror image for defense, invisibility for utility, and minor image for "summons"), 4 might be shapng fire (pyrotechnics for offense, fire trap for defense, continual flame for utility, and flaming sphere for summons), and so forth.
That would tend to make it difficult to balance, since at lower levels it's too powerful to pull out 5th+ level spells and at higher levels the lower-level spells are likely to be a waste of a combat action. You might instead want to make Lesser, Standard, Greater versions of the deck with 0th-3rd, 3rd-6th, and 6th-9th level spells, respectively. Requires picking a lot more spells, but it would definitely be easier to balance and price.
Good ideas all. Would you like to have a go at building a deck?