I think variety of experiences are beneficial. That could be the UK or further affield.
We've done AI but if we do, we leave the resort on trips or getting on a public bus to nearby villages/ towns. DS still remembers the jeep ride and markets from when he was 3. We've self-catered and made the most of local restaurants. We camp in the UK and have camped in France & Ireland. We are at a stage where we do some repeat visits to places that the DCs particularly like, in a few years, the joy of digging away on a beach will fade and our holidays will change again.
It is common in my county for kids to rarely leave their small town. They may get a trip/ holiday to the county's default seedy seaside resort, or for the better off a beach holiday to the type of resort where you could be in a warm version of Blackpool/ Skegness/ Weston-Super-Mere and not speak a word that isn't English or live on "British" food.
I remember one girl having missed school for a week to go to Bulgaria. I asked what it was like and she shrugged looked a bit blank and said the beach was nice. If it's the level of purely going to a beach resort and spending the entire time by the beach and pool, the wider benefits beyond a nice week swimming, building sandcastles and getting a tan which you could do at thousands of other resorts with the right climate and a coastline are being missed a bit.
The real value is knowing that the world is more diverse than your neighbourhood, but foreign holidays aren't the only way to achieve that.
I am very priviliged to have travelled to a diverse range of countries through Europe and Asia, but one of the great benefits has been helping me see Britain afresh. 5 days on the Trans-Siberian looking out on silver birches has really made me appreciate the diversity of the British landscape! Tibet has made me appreciate freedom of speech and democracy. Documentaries are great, but being there is incredible.
Going abroad isn't essential, but it is healthy to experience more places than you can count on one hand and they don't have to be far away.