don't know if you gave up or passed this, but make sure that you do all of the challenges, as these open up castles... especially getting gold on them if you can, I don't know if that REALLY makes a difference, but in my first play-through I made sure I had gold on EVERYTHING before I progressed...
1000+gs=16 - 1000gs=41 - 900+gs=11 - 800+gs=14
40k 28-09-2009; 50k 31-07-2010; 60k 29-09-2010
70k 27-12-2010; 80k 07-02-2011; 90k 31-03-2011
100k 18-05-2011; 110k 29-06-2011 120k 19-09-2011
130k 25-02-2012; 140k 03-03-2013 150k 06-08-2013
I'm slowing down...