I've never added the diazo. Like others said: completely dry coated screen, full exposure, completely dry again, emulsion blockout, post expo @ 2x initial on squeegee side, harden (if needed).
I don't bother with the hardener unless we're going over 300pcs and/or color changes are involved or the screen might be up for a couple days. Even then I really only notice the effects of hardening when printing with very high mesh/thin stencils, it has a very positive effect in that scenario.
I insist on using the pink for no other reason than thick coated Aquasol stencils, like for plastisol, will be opaque dark with the blue. They don't offer the undyed version in less than a drum so we use the pink. Funny you should mention the blue feeling "more durable", Richard Greaves told me that is done by emulsion mfg's for that very reason- we printers think it's more durable. So yes, I believe the color of dye is the only difference although different colors of emulsion, like different colors of mesh may/may not absorb light differently which could make a noticeable change in exposures.
I do keep a contact solution bottle full of the blue on hand for blockout so you can easily see what you are blocking out.
I wholeheartedly agree with Colin that the cracking of thicker stencils at higher o.c. is the only downside of Aquasol. But, I bet that "brittleness" is what lets us confidently soak our screens in a tank of plain water and blast out 60lpi dots on a 330/30 with a pressure washer. If you need a more flexible emulsion for those thick plastisol screens check out Kiwo One Coat. If you are printing DC/WB I'm of the opinion the screen should be on contact so no real issue with cracking there unless you are printing over seams and such.