I'm a little familiar with the area. My (since deceased) brother-in-law used to be the United Church minister in Centreville, and we would go visit them a couple of times a year when they lived there.
Yes, they popped over to Houlton and Presque Isle all the time to get groceries and for entertainment. I remember going to the theatre in Presque Isle with my sister and brother-in-law to see
Fantastic Voyage back in 1966 (it must have been a memorable experience to remember this event 56 years later).
These American towns did seem more substantial at the time, and travel was easier between the two countries. I agree though that the upper river valley towns on the Canadian side now seem more substantial than before, and that the corresponding American towns appear more lethargic.