The only benefit I think there is to a clear coat (future or anything similar) is to protect any weathering from being effected in the removal of the paint layer. The water attacks the hairspray layer (just like the shower attacks it in your hair) and it shouldn't make a to big a difference if it's over a clear or not. When I did the chipped up bed in my half track, I skipped this step and it completely ruined the wood grain effect below it so I had to go back and start all over again. The paint chipped exactly the same but I also scrubbed off the wood grain effect.
My guess Chuck, is perhaps your hair spray layer wasn't thick enough? Tamiya seems to be the best paint for this effect, Vallejo not so much. The Tamiya paint comes up in small, scale sized chips and scuffs, Vallejo tends to peel off in large chunks and sheets.
I use TRESemme, 'Tres Two' ultra fine mist right out of the can. There's no need to decant it and put it in the airbrush for me, the ultra fine mist works perfectly by laying on very light coats until I am happy with the amount.
I have still been able to get the paint to chip for a couple of days, although it may take more vigorous scrubbing, it still works for me. Try again with a couple more layers of hair spray and see what happens, I usually let each layer dry before laying down another.
but that's just my experiences with the technique, others may have differing opinions. :peace