LapLap

I was approached by just such a student on the air-side part of Valencia airport. I'm not sure how well the research would have gone in English but in Castilian we covered a lot of ground relating to my experience of Valencia as a tourist.
So yes, the authorities in Spain do allow such research to proceed. They even allow it to take place in the 'controlled' part of the airports.

On that particular occasion I had taken about 50 colleagues from London to the city for a weekend Christmas beano. Over the course of a Friday night the group dispersed more and more thinly into Valencia's famed and varied nightlife, pretty much all of them sticking out as tourists.
No problems whatsoever.
Even the guy who'd left the hotel without writing down where he was staying and remembered nothing about its location, or its name, ended up back in bed safely through the kindness and concern of a series of helpful locals. (From the historic town centre to the Silken would have required a lot of patient assistance)

So when the graduate student, through me, took data relevant to so many visitors, all of whom would have been fair game for a criminal, the only negative comment I had was how I'd been mildly screwed by a taxi driver on the way back to the airport (I'd stupidly asked him to drive by the CAC as some of the other passengers hadn't seen it and he took advantage of that to then go the long way to the airport... I really should have seen it coming!)

Admittedly, I haven't had the chance to return to Barcelona for a while, but not so long ago I went back to Valencia (Spain's third largest city) and did so in a wheelchair with my Japanese husband.
If anyone is going to give off a vibe as vulnerable visitors screaming 'ROB ME!' it's the couple speaking in English, where one fits the prime victim profile by being from the Far East and where the other is immobile and has a couple of bags stacked onto the wheelchair in front of her.

Despite all those times I've seen enticing looking bags slipped from tourists' shoulders and goods taken from people oblivious to the outside world in their unlocked cars (and it seems to me I've personally been witness to more crime in Spain than anyone else here - in addition to which I have a close uncle who was a policeman and am extremely close to a cousin who currently is a policeman - both of whom are very witty and have tons of great anecdotes) I didn't feel at all uneasy.
We stayed vigilant, we rolled through Valencia as tourists, we used the metro (which has EXCELLENT wheelchair access ^) and nobody targetted us. By avoiding a taxi we didn't get screwed over this way either - although this is usually easy enough to avoid by getting the driver to confirm how much it should cost right at the beginning... the onus is then on them to justify any major discrepancy. It's something I'd simply forgotten to do previously.