There is nothing inherently wrong with adding flourishes to your magic. I do it all the time to great effect. The key is keeping it "appropriate." What I mean is that when you do flourishes it is kind of tipping the fact that you are good with cards. That in turn tips the fact that you can manipulate the cards and then, what the spectator is watching, is a demonstration more of skill than of "magic." So, for instance, I just started doing an effect I call "Throwing Star." It is a sandwich effect where two cards(The Jokers) are tossed in the air and caught in a fan. When you pull the jokers out of the deck you realize that they have caught the spectators card in between them. The whole effect is a fun "show off" kind of effect so it is perfectly acceptable to add some flashy flourishes surrounding an effect like that. Indeed, many effects can be presented as kind of a demonstration of skill and still not ruin the effect. A tabled gambling demonstration is a demonstration of skill as opposed to magic and many of those can be as entertaining to the audience as a magic show. So essentially flourishes can be added to stand up and walk-around magic to a similar effect that long table spreads and smooth table faros add to a gambling demo.
Where I wouldn't use it are for card effects that are not really card effects. They are inherently impossible and therefore "Magic." Case in point would be something like "Twilight Angels," or something like "Anniversary Waltz." These are effects where something impossible happens to the card itself. In the case of TA the angel on the back of a Bicycle card moves around the back, in the case of AW two signed cards are fused as one. I feel you kind of tip the fact that you are using sleight of hand to disguise a gaffed card if you get to flashy in the moves surrounding effects like that. Indeed I would actually go a step further and say that you should barel;y handle the cards at all when performing those effects. They kind of warrant a minimalist approach. In theory, you shouldn't be seen to be handling the cards much at all, No shuffling, and No cutting what so ever, whether you do it in a flourishy way or not.
So for instance, with TA, I really like to sell the fact that the back is normal by doing a short ACR sequence prior to moving the angel around the back. In that ACR sequence I use moves that allow me to insert the card in the pack, square the pack, and immediately show the card has risen to the top. No shuffles or cuts in between insertion and reveal. So I guess what I am driving at here is that if you truly want to present a card effect as if it is magic and not sleight of hand you should go further than merely eliminating flourishes and fancy cuts from your routine. You should eliminate ALL cuts and shuffles from your routine. Ie. No double undercuts, no overhand shuffle controls, no nothing. If you want the cards handled after the card is inserted in the deck you can let the spectators shuffle, but you shouldn't be seen handling the deck at all.(or at least as little as possible.)