Yes, the dj element is front and center... but in an area saturated with legit, great quality dj's, and couples who are willing to spend on production and make it as much a part of the experience as the dj themselves... they will not book you if you can't give them what they want (aka the entire production). Now, regaridng sparks... unlike boston, where outsourcing sparks is more or less a necessity and the referral will likely be a pyrotechnic company... here, specifcally in NJ, if you refer them... you're literally gonna be referring them to another dj... who's to stop them from booking him doing everything through that guy. Let alone the venues recommended vendors will all offer the entire experience. In addition, if they're shopping around... you think they're gonna continue the conversation with the guy that doesn't have what they want? They'll just narrow the conversations down to the companies that do offer what they want. You'll never even get the chance to refer them to a source.
Now let's talk about landscapers... say you find 2 different options for weekly maintenance... 1 guy presents an option to just cut the grass and does the edging aka the bare minimum... another guy charges more per week, but includes seasonal clean up from down'd tree limbs during the winter and overgrowth, shapes the flower beds each year, weed control, leaf removal up until the last leaf drops and patio cleaning, as well as optional additional services like aeration and overseeding, shrubbery trimming, etc. Let's say I like that all inclusive experience option 2 offers. Guess what... I'm not calling option 1 to see if he can do it or if he knows someone that can do the extra stuff if I book him for just the essentials...i'm just booking option 2. FYI... this example is a true story of how I shopped for a landscaper.
Maybe I'm old... I don't know what the chocolate fountain reference is... but here chocolate fountains are provided by the venues... always have been.
