It seems that you have hedged your own position by using a very big IF in your premise. It also seems unwise to rely on your spectators' faulty memory when it comes to those among them who are bent on reconstructing your presentation in an effort to ferret out your method. Why would you want to give them any wiggle room at all?
I completely and totally agree about keeping things simple. I completely and totally agree that that there's no need to use complicated methods when simpler methods are a better choice. But the part you keep missing and failing to address is whether in fact a simpler method (and I agree that your method itself is certainly "simpler") really is a better choice in a particular circumstance. You have to have both components. Just because a simpler method exists does not automatically imply that it is also the better choice. It's absolutely wonderful when they are one in the same, but there are many times when they are not. This is especially true when it comes to magic. (It also applies to everything, BTW: it is definitely possible to kill a grizzly bear that's attacking myself and my family with something as simple as a knife; but I'd prefer the slightly more complicated shotgun method given a vote towards a better choice under the circumstances.)
While we're on the topic of simplicity, what's simpler: concealing a set of selection buttons for a second or two while you tap them? Or keeping the screen in full view at all times from the moment you bring the phone out and concealing nothing? There's just something about bringing the phone into view with a "normal" (appears that no app is running) screen and letting the spectators see that from the get-go (well before the card is named) that IMHO makes the effect so much stronger than not showing them the spectator the screen until after the card is announced.
But what about all that phantom tapping you say? Yeah, I guess I have to give you that one. If I blatantly tap the screen a couple of times for no apparent reason in front of the spectators, that definitely would not make one bit of sense. And it would look pretty danged weird too. Of course, if you were doing your job correctly as a magical engineer, you would find a way to incorporate the two required taps into the routine itself and they would not only go unnoticed, they would in fact be motivated when executed by a performer. For example, since no app is supposedly running when you bring the phone out, it makes perfect sense to tap the screen to launch the "magic deck of cards" app (even though it really is already running.) So there's one free well-motivated tap right under the spectator's noses. Now let's take that one step further. Suppose an alert or a message or something appears on the screen a little while after you bring the phone out (but it's really coming from the magic deck of cards app.) You'd be given another free tap to dismiss the alert - another well-motivated tap that the spectators have undoubtedly done themselves many times before too.
Now put it all together: Start the app running and bring out the phone. Set the phone in front of the spectators as you begin talking about their favorite card (forgive the lame patter cues; I trust you could do better. Like Indiana Jones, I'm making this up as I go along.) As you set the phone down, you touch the screen to get the (already secretly running) app to start a 20 (adjustable in the software) second timer. Just as you have the spectator name their favorite card, a text message (choice of interruption and contents therein also adjustable in software) pops up. You dismiss the text message with a quick tap (on the quadrant that secretly selects the suit.) You then launch (as far as the spectators know) the magic deck of cards app with a second tap (conveniently with a quick tap that secretly identifies the value.) It's all presentation from here.
IMHO, that's way stronger and more than justifies the more "complicated" method since nothing needs to be concealed - even for a split second. I'd also be lying if I didn't say I really enjoy performing any effect where the spectators can be burning your hands as you do the dirty work out in the open and right in front of them and they still don't suspect a thing. Being able to actually (albeit casually) draw their attention TO the (secret) dirty work (rather than misdirecting their attention AWAY from it) is almost more fun than magicians should be allowed to have. I'm actually starting to like this. BlackIce2x: when you're done working on the effect that started this thread, let's talk!
In practice, it's really hard to make things simple. But like Albert Einstein famously said "Make everything as simple as possible - but no simpler."