Like you I will be heading to Spain this summer but as of now only planning a day or 2 on the beach. Here in the United States I go to nude beaches all the time so it is not a big deal to me so I am not sure if I will pursue a nude beach or whatever beach is the closest for a relaxing day.
As for your question about getting overly turned on by seeing all of the great looking cocks, pussies and butts. 1st of all things happen like that especially the 1st time and maybe even the 2nd and 3rd time you go to a nude beach. Generally the beaches that I go to you very seldomly see a full-fledged Boner just blowing in the breeze. If perchance you do get overly excited it would probably be wise to sit down, cover up or take a quick dip in the water that will generally calm you down fairly fast. Most guys do not normally go around strutting their stuff at any nude beach or club that I have gone to.
As with anything there is a proper time and place for almost anything. At the beach that I most often attend there is clearly a heterosexual side as well as a swinger area but the most popular area is the gay and lesbian area. Heterosexual and swinger area you very seldomly see a full-fledged Boner but you might see somebody a little bit excited and possibly dripping a bit. The gay and lesbian section is quite different. There is lots of advertisement going on there and you see a lot more semi erect cock's then the other parts of the beach. Sexual attitudes and sexuality is quite different in that area and it is very common to see a group of guys in the water having a great time playing with each other. Nowadays flat out sex on the beach is frowned upon and the Rangers have actually given people tickets for sucking on somebody's cock or whatever. I must admit I have gotten and given quite a few blowjobs especially in the water but on occasion on the main part of the beach if it's done discreetly.
Hope you enjoy your trip and do not get too hard. Even if you take Viagra so that you have a little more staying power you should be able to keep that under control most of the time until the right time pops up sort of speak. Feel free to contact me directly if you have any more questions.