This is coming from a Traktor Perspective
4 Deck mixing in any scenario is really risky IMO. The more decks the bigger chance things go wrong (songs trainwrecking, over lapping of same color sounds etc.). I spin 100% EDM from Dubstep, house, electro, prog, breaks. I do create a lot of mashups using all 4 decks BUT i make my mashups pre-gig record them. then just stick with the 2 deck format. I do however use my sample decks for adding in extra percussions, little vocals riffs basslines, or even 1 shots for transitions.
When it comes to gig time…its all about K.I.S.S.
From what i know of VDJ the Samples work a lot like effects where you trigger them as oppose to full fledge sample decks. I remember reading somewhere that VDJ will be introducing actual sample decks in their latest version.
At the end of the day it doesnt matter if you make mashups on the fly or prerecord your own mashups…the crowd doesnt care what you are doing as long as it sounds good.