I will be visiting Barcelona, Spain and have read about the Aerobus from the airport. Would I have any problems with 4 suitcases on this particular mode of travel. I will be staying within 2 blocks from the Playa Catalunya bus stop. A taxi ride seems so expensive.
Buses are designed to hold a lot of luggage so bring your four bags.
I don't know if this is a relevant comment; you be the judge. A couple of years ago I was on a bus which ran from Sorrento to one of the towns further south on the Amafi Coast. The bus made a number of stops along the way, people getting on and off. When we got to our destiantion, one of the other passengers discovered that his suitcase had been removed from the luggage compartment. I don't know if this was an isolated incident or not, but it may be something to keep in mind...try for a window seat on the same side as where your stuff goes so you can keep an eye on things.
The Barcelona Aerobus has a luggage rack inside the bus, not below. It would be tough for someone to walk off with your luggage without being noticed.
I've seen a couple of times recently when people said to watch out the window at stops. If somebody runs in and takes your bag and runs off what will you do, other than get a sinking feeling in the pit of your stomach?
The bus won't be an issue. The problem will be getting from the bus stop to your hotel with 4 suitcases.