It's funny how I think a bit differently than you when I design my cards, just goes to show how many approaches there are.

Agreed, but that goes for the design team as well, it's printed right there on the playfield most times, no need to put it on the card. I leave it off.

2. Use high-quality 300dpi artwork that isn't in the game, instead of duplicating what's on the backglass or playfield. I'd make an exception for small art that could be highlighted, like the babe in the boat in Fathom.

Agreed on 300dpi, and I'm while I'm not big on straight up duplicating, I think it's important that the tone of the art matches the game, and ties the playfield and the translite together. There should be a stylistic link between them all.

3. Make the credits as large as possible, without obscuring the artwork.

Less is more, too much text is clutter to me. The card should have no more than a few focal points. So I agree on making text legible and clear, but don't care for the design team credits or a ton of copy.

4. Only one image per card; keep it simple.

I prefer a composition over a single image, something original, while still keeping in mind the above clutter and style thinking.

5. Include the year the game was made

Agreed, year is great. I also like to include the number of units produced if possible. I get cheeky with it and put things like "Machine 1/5000". Other key info is the Free Play text, it's supposed to be a pricing card, and I like it clear that my machine is on free play.

Just my approaches, no one person's opinion on this is any more valid than anyone else's, just a matter of personal tastes and whims.

I just (finally) posted my Shadow alternate translite that I've been working on, and as part of it I did some instruction/free play cards. So here's an example of one of my cards that hopefully sticks with the principles I laid out, just like yours stick with your list.

Instruction-Cards.jpg

I don't want to hijack your thread with my design, but you can see the translite here:

http://pinside.com/pinball/forum/topic/the-shadow-new-original-alternate-translite-speaker-panel-cards

to see what I mean about how I like to tie the card's style into both the translite and playfield. So in this case the imagery is related, but not exactly copied, and the colors and fonts pull in some from the playfield. The "Free Play" font was chosen because it feels similar to the Bally logo for instance, and the title font on the instructions comes from the scenes area of the playfield, colors are from the apron and playfield, etc.