Hey Marine 8. Thanks for the great advice. Took it up and rang globuskontiki when I got to Barcelona. They were great - courteous, friendly and gave good advice. They took no deposit, and picked us up from the hotel at the agered 6am. We were driven the 40km to the flight spot. We all got involved in inflating the balloon, which just looked spectacular (quite apart from the scenery around where we were).
However, the winds started up and they eventually decided it would be too risky to go up that day. A huge disappointment to be sure after being so close, but to be honest we all really enjoyed even heading out there and seeing it all happen. They then drove us back to the hotel (the return car trip just cost us 10euro).
So, I'll definitely do it again when I'm next in Barcelona. Thanks for the great advice.