If you want to hone the skills, the Trials bike is a step in the right direction.
Look at the riders that have crossed over, Meeriman, Jarvis, Blazusiak, the things they can do on a MX or Enduro bike is incredible. The other magic thing about a trails bike is they don't wear out. They may get knocked around a bit, but you won't be doing engine freshen up's every season or replacing tyres after every 2nd race.