I really like the AC Santo Mauro Hotel in Madrid, and find it to be a unique property. It's much smaller than the Hotel Arts, more of a boutique, so may not have as broad of services, but I really enjoyed my stay there. I've heard great things about the Cotton House, but haven't stayed there.
I think there are a lot of great day trip options from both Barcelona and Madrid.
From Madrid - Toledo is a 30-minute train ride and a must-see. Segovia, Salamanca, El Escorial, Avila are all within 2 hours from Madrid.
From Barcelona - Girona is 45 minutes by train, the Dali Museum in Figueres is about 1 1/2 hours, the Costa Brava has tons of beautiful beaches, Sitges and Tarragona are both within an hour or so to the south.