That's one gorgeous holster.  I don't know how you got that finish either, but keep doing it because it looks great. 
I know what you mean about the foamy resolene.  I have to wipe mine down the same way, and it's easy to get a blotchy or uneven finish.  An airbrush is one solution to foamy brushed on resolene.  I really like the airbrushed resolene/water finish, when applied evenly.  Just be sure to wear your respirator, as with any sprayed product.  I really can't see the glossy/satin spots in your pictures... Besides, after being worn in the pants a while I don't think you'll notice it anyways. 
I can't really recommend anything on the exotic gluing... I've never used Barge or exotics.  I have some Weldwood contact cement, and Tandy 'tanners bond craftsman contact cement'.  The Weldwood goes on much thinner and evenly, IMO; But I think the tanners bond stuff holds better (it's just more bulky and leaves a more visible line on edges, in my experience anyways).  I'm not sure which one is closer, if either, to the Barge formula. 
I think you'll be your biggest critic in regards to this piece.  This holster looks great!  I've got a request for a left handed IWB coming up.  I'd be very happy to have mine turn out nearly as nice looking as yours here. 
Nooj