Well, airport fees won't be the same in BCN than REU or GRO. Morever Catalunya has bought Spanair, and Vueling is merging with Clickair with the suport of Catalunya and Iberia. Vueling/Clickair is also doing codeshare flights with Emirates.
easyJet was interested in BCN but they've changed their mind.
Ryanair is probably realising that secondary airports are not good anymore.
They have just asked Valencia 4 Millions euros per year up to 2012 in order to come back with a base, but unfortunatelly for the arrogant MOL, Valencia is not very interested in this "low cost offer".
2 Years ago Ryanair was also saying they would build a major base in Castellon (close to Valencia)... now that's all gone.
I think Michael O Leary would like to set up a base in Paris (I mean Beauvais
), it seems to be very difficult to fight against the french working law. Maybe they'll come to CDG who knows ? they are almost as expensive as Air France (but the service offered by Ryanair is a total !!!!, going worse and worse every year)...