To me, Mull of Kintyre represents a Utopian ideal of simpler times in a simple, ideal place. A Camelot of sorts.
A beautiful thought and it seems most obvious that Mccartney was drawn to this area for several reasons. Sheer natural beauty, a laid back lifestyle and the pleasure of being with his family, loved ones and friends.
In short there is simply not, a more congenial spot. For happy ever aftering.