We honeymooned in Benidorm in September, 1961. There were a few high-rise buildings as shown in your more recent photo (the upper beach). That was when the building boom there was beginning (mostly Germans).
The first photo (from 1963) is the lower beach (i.e., below the Roman steps). Hotel Miramar, our hotel, was across the road from the lower beach.
We went back 25-years later: the 3-story Hotel Miramar had been replaced by a high-rise Hotel Montemar. The owner was the same. When we identified ourselves he invited us to the midday meal that was being served and presented us with our story to a group of German Tourists on a Group tour.
Some older Germans pioneered developments in and around Benidorm. Thanks to Generalissimo Franco many WWII Luftwaffe Pilots became familiar with the area - there was an R&R resort for them there