Second: I did not think they OWED us anything. Had they offered to pay for our tickets, we would have said no. Had they offered to feed us anything more than a very cheap dinner, we would have said no or offered to split the cost. All I wanted was the gesture. Because they were asking us to do something that would be a financial imposition IF WE SAID YES. Yes, I totally GET that we could have said no.
Not offering to pay was not rude of the couple. Some people (maybe not you guys, but other people) would take them up on the offer and maybe they didn't want to make the gesture of taking you out to dinner or splitting the ticket if they weren't prepared to do so if you said yes. Making an offer that you aren't willing to follow through on is rude.
You and your husband didn't have to go to the concert, you could have declined doing that. True, they asked you to do something expensive, but as long as they didn't promise to pay beforehand and change their mind, they were not rude by doing this. You also had the right to say 'no' and that would not have been rude.
I'd also be interested about how you got roped into driving. As the people who invited you, I think they should offer to drive to the event. I feel it is a little rude for them to suggest you drive when they invited you along to the event (if this is what happened). The really rude thing this couple did was eating in front of you and not offering you any food. Because you went through the trouble of driving them to the even, the least they could have done was offer you some food or a cup of coffee.