not hard, just time consuming..and little patience 
i haven't tried those particles, but i tried add putty into flat paint and spray using airbrush at long distance, works fine

you are right, a decent diecast with details just cost around rm300-400, while a car kit cost around rm100, reason is because not much people into car modeling, that's why the price is not cheap...although it is much cheaper in HK, i got my tamiya fairlady z nismo just for around rm70, but of course not included Photo-etch set, paint and flocking and etc..estimated each kit i usually spend around rm150-rm200 for everything, BUT there's some difference between model kit and die-cast, both had pros & cons 

and owning a diecast & buidling a model kit had different kinda satisfaction as well

i have seen model kits much much more detail than diecast, reason is that diecast is also made by hand, some are mass, some are limited production, and usually the limited one are very expensive. 

each diecast had a total building time, let say 20 hours (not including designing the mould & diecast, just paint & construction time), they try not to spend too much time on it or else they rugi workmanship, BUT you can spend many hours on a model kit, those super detail model kit takes around 1-2 years of building time, so you think which is more detail? 

here's a VERY detail 1/20 F1 model kit, built by a japanese, you wouldn't see such detail in a 1/20 diecast 






more pics here:
http://gdist43.com/gallery/index_23.htm