Best parties I ever got were out of a cart in Orlando. Muffins the size of my head and arm sized eclairs with real custard. Best pulled pork sammich also from a cart in the upper keys. Of course, the problem with carts is that they are transitory. Regs changed in orlando, BBQ either moved or went to catering. We used to pick up roaster pans full of the stuff for parties before they moved. Hot dogs carts in dc do not leave me with such good memories.
Anyway carts can absolutely be roadfood. And a lot of the great places are ‘get it while you can’ because you never know when a place will sell or someone will retire and leave you with a second rate cook and memories.