Being "flashy" indicates to the audience that you have the ability to skillfully manipulate cards and the audience will attribute any "magic" to your skillful abilities.
Contrast two presentations.
In the first, the spectator inserts their card in the middle of the deck and the performer does a series of cuts that would make Sybil proud and then has the spectator turn over the top card to reveal their card. I suspect the reaction will be a "wow, you're really good with cards."
In the second, the spectator inserts their card in the middle of the deck. The magician places the deck down on the table and asks the spectator to put their hand on the deck. The magician then places their hand on top of the spectator's hand and asks the spectator to think of their card and imagine that their card is melting up to the top of the deck. The magician lifts his hand and the spectator lifts their hand. The spectator turns over the top card and sees that it is their card. I think the reaction will be a "What the heck! How could my card have come to the top... you never touched the deck."
That being said, I think a magician should be able to do basic cuts, flourishes (fans, spreads, etc.) and shuffles. That gives the audience a sense that we are professional. Unless you are Lennart Green, who amazes even more by the haphazard way he appears to handle cards.