I was worried about it too, but went all in two years ago on Garmin GPSmap 7612xsv MFD. I could not be happier, have not had any problem. I do OK keeping my hands clean, but in the rare event a smudge ends up on the screen in the wrong spot, I use a screen wipe and touch it up quickly. I end up doing that like once every 25 trips or so.

For me, after 2 years, it's a no-brainer, the ease of use of the touch screen outweighs the drawback.

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"Laugh if you want to, it really is kinda funny, cuz the world is a car and you're the crash test dummy"
All Hail, The Devil Makes Three