In one of my first spanish classes the teacher explained this custom to us. I thought it was such a sweet act. So, if I was in Spain, then yes. I would love to be whistled at. But, here in America, it tends to have a different connotation. Here in America, I do not like being whistled at. When guys do it here, it has a message that the woman is "cheap".
Person like me would never want to live in a place like Spain then. If you ask me what i think about public compliments like whistling? according to me compliments are supposed to be very private anything which is publicized looses its real charm therefore if i am a citizen of Spain the way i would go about giving a compliment to a man whom i don't know from Adam's will be walking up to the handsome man and compliment him right on his face this might give a start to a new friendship or just a pleasant memory down my lane of memories........
Compliments in Spain can be very public indeed. I know from stories that Brazil is much 'worse' than Spain.
In Brazil it's more agressive but still a cultural way of appreciating beauty. To give a guy a compliment straight forward is a very nice way. The only problem here is that they are not used to women being direct.
I know I did the same thing when I was single and it's obvious how many guys feel uncomfortable when you tell them straight away, you like them.
What does work is, compliment them at the end of the night and then walk away....to give him that pleasant memory you mention.
Guys used to whistle at girls they thought were attractive as a compliment & that is how I took it & it would make my day as it was harmless! Sadly because of so many uptight females the habit seems to be dying . I certainly wont complain if I get whistled at when we go to Spain !