Hi Sam,
How about trying another method for applying weathering powders to smooth paper? Rather than using hair spray to stick the powder to the surface, you could try spraying the brick paper with Testor's Dullcote, and this will give a rough surface (when dry) that the powder will stick to without any other help. Practice on some scrap paper first, though, to make sure the lacquer won't harm your good work so far. I think you'll find that the powders, when applied this way, will give you a much more subtle effect - just use a soft brush and apply very small amounts at a time.
I've only just found this thread and have read through the whole thing! You've made good use of the space available to you, and it's all looking pretty good.