Visiting nurseries is one of our favorite things to do while we are out of our area. We also like going to grocery stores and picking up goodies that we don't have in Texas.
DH's family live in Seattle Area. They truly have some wonderful nurseries out there! They are the kind that present their pants in such a way they make you want all of them!
We have purchased many thing from Seattle area in the past and learned the hard way that even though their things say "Full Sun" most can't take the heat we have here in the South, let alone our full sun. But I have some treasured gifts from my MIL, amaryllis bulbs and clivia that thrive.
I think your road trips plans sound like a fun one!! I would find it hard not to over buy to the point where there would be no where for me to sit!