What this boils down to is that with a Nexus card, if you wait in line for 15 minutes.....that is a long wait. At Peace Arch, the waits are absurd and seeing the lines, 2 hours would not be unusual (and it might even be more) and that is EACH way.
So a day trip to the states (assuming that they are hitting the outlets) takes a trip that is a max 2 hours each way with a Nexus card to one that could be way more than 4 hours each way without. So if you are going or a day shopping trip, 8 hours of it is sitting in a car.
FWIW, getting a Nexus card is not difficult. You fill out an application and pay a fee. A month or so later, you get a letter that invites you for an interview. At the interview (where you talk to both Canadian and US customs agents), they go over what you are allowed to take over the border and the rules of the program. They take your picture and fingerprints. They may or may not do a retinal scan (this allows you to use the Nexus lanes at airports), not all offices have the facilities to do this, I got mine at YVR after the fact. You do not have to be interviewed at the same border, I had mine in Champlain NY, but normally use Peace Arch or Truck Crossing in BC. A couple weeks later, you get the card in the mail.
As this is a trusted travelers program, you are not allowed to screw up. Customs agents DO have the right to do a more thorough check and can pull you aside if they suspect something (I have seen this done several times from the Nexus lanes), and if you have something that you are trying to slip across the border, they can and will pull your Nexus permanently.
You do not need to be a driver, or have a car (even though they do as your car make/model and registration on the application). The card also allows border crossings to be expedited at airports, and I most recently used it coming back from Mexico. I believe that there are more countries that are also in the system now too. Not sure which though as I have only used mine in Canada and Mexico.