The problem with coastal towns of any size (having grown up in one) is that there is an odd combination of high property prices and lack of decent jobs. Also a fair bit of minor anti-social behaviour due to lots of pubs and tourists, and as mentioned, people down of their luck heading to the end of the train line, or picking somewhere scenic and warm to rough sleep.

If you want somewhere properly tranquil and quite you need places that are more villages (and full of second homes).

My vote for somewhere suitable is St Ives.