I think you've just convinced me. The idea had been that the kids would rather be on a ferry than stuck in the car, but at least the car would be going somewhere.

We used the Lynden crossing last time & it wasn't bad at all. As I understand it, we also don't need ESTAs if we cross by land but we do if we come in on the ferry. Multiply that by 5 (I think they've all expired now) and that's quite a saving.