.. here’s how.
Instead of ‘dual spec’ for 1000 gold, make it alternate specs (plural) for 1000 per spec. This way you can drain people of more gold while catering to classes that really could use more than two specs.
Prime example, Paladins. Tank spec, DPS spec, Heal spec and PVP spec. (Gee, I wonder how I thought of that?)
Other examples, Druids with Feral tank, Feral DPS, Heal and Boomkin specs.
Mages with Ice, Fire, Arcane and hybrids of those.
And so on…
Benefits to Blizzard?
People have more gear sets to build keeping them in the hampster wheel longer. You also take 1000 gold out of the game per spec slot (think bank slots) the character buys.
Optionally, you could have a scaling cost; 500 gold for the first one, 1000 for the second, 2000 for the third or some such scheme.
Make it so!