Curious to see how others structure their paid marketing efforts in Marketo. I've seen many different ways after a couple of years of consulting...and have never seen two setup in the exact same way. My personal preference is to have one program per campaign run and use various URL parameters to slice up results. I find it makes things easier from a reporting and setup perspective...but happy to be proven wrong.
Your way definitely makes sense. I would think that would be the best way to track cost metrics as well. It will be interesting to see what other people say.
Here's one way to do it: Marketo-Nation-Talks-Advertising - YouTube
Smartlists within content programs (as one use case) that keeps a running count of conversions via paid, and then an example with a standalone program for success and revenue credit