Hubs with dissimilar flange sizes are annoying to build, you have to bend half the spokes fairly strong to get them to clear the big flange.

Assuming that it's the disc side that has the bigger flange - yes, that will improve the brace angle, just a tad. Haven't done the math for it, but I'd guess it'd only be by a few percent. Whether it's "worth" it or not is really hard to tell.

False economy or not depends on how you value your time, and what you know about the condition of the spokes. I've disassembled and rebuilt a bunch of wheels. For fronts it's a fairly safe bets. Rears are more dodgy.

24 spoke being sketchy for discs is a bit misleading. The big thing is available spoke cross section, which you get from no of spokes times gauge. If you'd do 24@2.3 mm gauge spoke, you'd get as close as doesn't matter to 32@1.8mm gauge, and no one would question that build. Sure, more spoke are safer if one breaks, so you'd have to be OK with that risk.