The best investments in any beach/coastal resort are the apartments/villas that are beach front or have amazing views. The further away you go from the beach 2nd, 3rd line etc the less rentals and the less chance of resale ability you will have. For pure investment anything else i think is risky.
New and off plan developments are and will kill many coastal markets in time with over supply. Bulgaria and Spain had very little regulation.
Turkey has slightly better laws regarding this i guess with 20% building density and many developments being under 3 or four stories.

If you are buying anywhere else i feel that it should be more of holiday home/investment.
Sunny Beach is a great example of this. Turkey will follow in Sunny beaches footsteps i would think in the next few years. The real winners in Spain are the front line properties. This will be the case in Turkey, Albania, Italy etc.