Nothing wrong with the countryside at all, I love it! However my idea of a retirement home is not in a chilly backwater in Bulgaria, but I did say, if you read my post, that it will suit a limited number of people who like the life and culture in rural Bulgaria. For me, it would be just too miserable in wintertime, but I accept that that is just my view and that others, including yourself, see it differently.
As for rural Bulgaria being a good investment, it is probably a lot better than the overpriced coastal property, but only in the sense that the low prices mean that you have less to lose. It is simply a fact of the market that rural houses in deserted villages (see much of inland France) comprise a stagnant market with little or no investment potential.
And before you start to disagree, I know that the countryside, particularly in summertime, is very pretty and a beautiful environment for a relaxing couple of weeks. But would I live there? Not likely, and neither would most people; the reason that so many houses are available there is because the Bulgarians have deserted them. This is the story in many countries in Europe, including Ireland -- in spite of a property boom in Ireland there are still loads of empty houses in places like Mayo and Leitrim that nobody wants to live in.
All my life I have kept out of trouble in the property business by thinking with my head instead of my heart; that means staying away from these kinds of properties, nice and all as they are. Nice places, wrong location, location, location.
And unless I am very much mistaken, this thread is about property investment, not property buying. Two entirely different things.