The greed and seedy behaviour of Real Madrid and Barcelona has destroyed the potential of many clubs in Spain. The likes of Valencia, Sevilla, Athletic Bilbao, Real Betis and Athletico Madrid have suffered due to the financial abuse and corruption of these two clubs. The fact that Diego Simeone has been able to win La Liga title, and make two champions league final under these financial constraints has been a remarkable feat. If Barcelona and Madrid had to share revenue like EPL clubs do; they would have not obtain anywhere near the success they experience over the past decade or so.
I can see La Liga going the way of Seria A. A once formidable popular league reduced to insignificant league which barely gathers attention. Milan derby was once the biggest match in Europe, now, who cares or even watches it.
There are only two options for other European leagues in the future; either create a European superleague or rebrand their leagues allowing middle table teams to flourish and create a competitive league.
The Premier League has also suffered from the financial clout of the Spanish giants.
David Beckham moved to Spain. van Nistelrooy moved to Spain. Thierry Henry moved to Spain. Arjen Robben moved to Spain. Cristiano Ronaldo moved to Spain. Fabregas moved to Spain. Mascherano moved to Spain. Xabi Alonso moved to Spain. Bale moved to Spain. Modric moved to Spain. Luis Suarez moved to Spain. Coutinho moved to Spain. Hazard is about to move to Spain. You could make a competitive PL all time best XI just out of players bought by Barcelona and Real Madrid. Going the other way, the PL only bought La Liga players from lesser teams like Torres and Aguero, or rejects from the big two like Makelele, Deco, Robinho and Pedro.
Spain has consistently taken all the best Premier League players, year after year, for the last 20 years. Losing that much star power has definitely weakened the Premier League on the pitch as well as off it in terms of marketing. But even though they constantly snatch up all the best players the PL just keeps growing. It's a juggernaut now

you take all the best players and STILL Cardiff City vs Fulham makes more money than Real Madrid vs Atletico Madrid
Barcelona's wage bill is more than 1 million euros per month higher than Man City's, and still their fans blame the PL's money for its success
