if raytraced materials  with IDL takes hours to render then it would be better to render it out without reflected materials. then in a seperate render we render out only the reflection. then in a software like photoshop we combine the renders together.
if it saves 5 hours .....why not? :) 

the same with lashes. i rather render without lashes and then combine it in photoshop or even paint it in photoshop then to whait 2 hours longe.