For the first 7 years of my life we went to Abergele for our holidays. I'm sure the weather was mainly rubbish but I don't recall ever being bored, we went to the beach, rode the Great Orme cable cars and tram, played crazy golf etc.
And if people started going back to places like Abergele, Rhyl, Morecambe etc, they wouldn't be run down dumps as some of them are (apologies to Abergele as I've not been there for yonks, but I think that's accurate as far as Rhyl goes), rather the money brought in would make them once again nice places.
Blackpool would always be Blackpool but you don't have to go there, it's one place, you know what it is, go if you want that, don't if you don't.
What most people would be left with would be fewer, but higher quality, foreign trips. And I don't think that's a bad thing.
Going on foreign holidays seems to be up there with Netflix subscriptions with boomers telling young people why they can't afford a house when the average one is 9 x average incomes. Back in the real world its usually cheaper to go abroad than holiday in UK even with higher travel costs. Even a cheap place on the South Coast is often twice as much as places to stay in the Med. Going on holiday to Cornwall for two weeks is a sign of wealth not financial prudence. If or when I have kids I might take them to the South Coast once or twice to experience places I went to as a child but it certainly wouldn't be to save money.