All of the above sound right. I used to do a lot of propping on shows so I'll throw out a few ideas.
First off, I'd suggest buying a deck which you intend to wreck and if you only need a few cards for setups, identify them and make your job smaller.
Tea and smoke will age anything, although you have to be very careful and not get the deck too wet, unless you're willing to iron them... Actually that's not a bad idea, although some scorching will likely ensue.
I aged a deck for a play once and used fine sandpaper on edges to soften, then after spreading them out in several mail racks (those wire divider things used in large offices with little metal walls so the cards can be stood separated) spritzed with tea and smoked them dry (cedar chip embers in a metal dish). Smoke is great but SLOW and very space intensive.
That said, when aging thick paper, oil can work well very quickly. The trouble is, the protective lamination on most cards blocks absorption, but if you sand the cards very lightly, they will absorb easily. To stain, try mixing fine ash or soot and a fat dollop of brown/yellow watercolor into any dark cheap oil, and then smooth a thin layer over your hands... then start shuffling shuffling shuffling, breaking and riffling the cards like a poker dealer. In this way it's easy to gauge the color and to control the results. Be sure to wipe off excess oil before the shoot to prevent hotspots when lighting. And because your actors will get even more slippery than they are naturally.
Umbrae's coffee idea is also excellent (the older and more overcooked the coffee the better), just spread them out on sheet and spritz on, let them dry, flip and repeat.
If you're in a mad rush and need results in an afternoon that might smear a bit if scraped, spray on a layer of yellowish varnish/sealant/glue, allow it to dry, then apply a very thin stipple of dull beige acrylic with a coarser sponge to diffuse the color, then break the cards.which will move some of the pigment around. That said, this rush technique will give them a shitty impermanent texture.
Also, I know that for film cards do get broken over table, which is especially good if they're going to be handled a lot on camera by actors.
Good luck! Can't wait to hear how it goes..
Scion