Seattle Eastside is home to numerous contractors working at Microsoft and other hi-tech companies) or are they vacationers/tourists who stay for a week and return home?

Think of the impacts to pricing when applied to simple supply/demand...you (the government) artifically limit the supply (available STRs) -> prices for STRs go up due to limited supply with the same influx of renters -> more people turn to hotels as the more affordable option -> properties lose their ability to support STRs due to increased vacancy -> property values decrease; not to mention that many tourists opt to stay at AirBnB BECAUSE of their unique experiences; strip that away, and you've removed of a facet of your tourism industry. 

I live in Gunnison, Colorado (a small college/tourist mountain town) and the real estate prices are high here so it is hard to find a good deal (I am interested in buy and hold).

I get access to private deals like that in several tourist hotspots across the world but there was a limit to what I could do with my own money.Investors asked me if they could invest with me.

You have the tourist game, but don't forget hospitals and traveling nurses.My sister works at Cape Cod Hospital and talks about all the traveling nurses and therapist that come through.

However, Catalonia may be a little tricky these days (protests, aversion against tourists in Barca)...My dad backed out of Spain, but that was in the 70s: the apartment blocks he saw were too secluded back then...Anyways, good luck and hope you'll find something nice :)

One more thing...I would love to do a complete renovation at the quadruplex and start short term renting the units (we live in a tourist destination).

To piggyback on that, how well do AirBNB properties do in areas that are close to a city that isn't necessarily a tourist attraction area and not close to big employers in the area? 

Beach apartments in tourist areas. 

It is fantastic, but our baseball team is called the "Tourists" for a reason, I guess!