After a few years with the 520 I went through the touchscreen debate and talked myself into the 830. Over the last two years I've had zero (that I can recall) issues with screen sensitivity, even when I dumped my water bottle on it by accident. And I agree with Seattle Forrest - I can't even imagine scrolling or zooming through a navigation/map screen with buttons, something I do frequently. And the ease of getting to options, setting, etc. Heck, just swiping to change screens on the ride is a major advancement - no fumbling for buttons, I can switch screens without even looking at the unit until I'm ready to take my eyes off the road. Honestly, I can't imagine going back to straight buttons at all, any more than I can imagine going back to a non-touchscreen phone. Is it worth the (now) $150 extra? That's tougher, but I would probably choose the 830 over the 530 again even with the extra $50 off. Obviously, YMMV...
edit: one downside is fingerprints on the screen. I often take my unit off to rub it on my shorts to clean the screen, otherwise I get glare. So that's a downside, but it doesn't come close to offsetting the upsides in my opinion.