There's no hard and fast rule. Do what ever suits your character. Madison can incorporate flourishes into his magic (his 4 ace production), but then he's honest with the spectator that what he's doing is all sleight of hand.
If you're busking, just standing with a deck of cards in your hand won't get you very far, but if you're stood there flourishing you're going to attract attention, from there you can proceed with your magic routine.
In the case of Dynamo, he uses his flourish as a control. People like how he's doing the flourish or the robot dance he does with it and this makes them ignore the fact he's controlling their card to wherever he wants it. To this end, his flourish is misdirection, and it's a clever sort as instead of directing the gaze away from the deck like traditional misdirection, he doesnt care if they burn it. He's controlling the card right before their eyes and they're entertained by it.
It all depends on character. If you're trying to convince someone you have special powers, flourishing will just make it look like you actually just have way too much time on your hands, and may detract from your mysterious character. If you're honest and say you're using sleight of hand then proving you have fast fingers is nothing to be ashamed of. It doesn't mean your magic will be any less hard hitting.
Try both, see what suits you. I believe you can incorporate flourishes into tricks as long as you present them properly. David Blaine used Daryl's Hot Shot Cut as a trick and it worked fine. I've also used it in an ACR and people have liked it. I do think that things like flourishes and packet tricks can be a bit selfish if overdone though. You need to involve the spectator in your magic, not have them just stand there while you show off. So, everything in moderation and make your own rules.