I think its each to his own, just because your set up costs peanuts doesn't mean its better or worse. To say people who spend £500 are stupid is quiet frankly insulting.
Should I go around saying anyone who uses their phone selo taped to the bars is obviously a council chav on benefits!! Come to think of it they probably get a £500 sat-nav for free

Rant over and forgotten about
For me, the main thing is planning routes. Particularly on Euro jaunts. You can spend a few evenings studying the maps and biker sites for the best roads in an area. Load up Basecamp software and construct your routes to suit, then load them up on the Zumo and away you go. I get thanked by my friends for some cracking days out.
There's no stopping regularly to consult a map (done that at 22.00 hrs in the rain lost in Germany - I vowed never again)
Its all wireless to the headset so no forgetting to unplug any wires attached to you when you get off the bike. I've got loads of music loaded up so the phone just sits in my pocket forgotten unless a call comes in and then its all on screen. The screen is large and bright enough for my aging eyes as on the phone I'm always having to put my glasses on to use it!

As I said the touchscreen works better with gloves on than off, my iphone needs gloveless fingers!!
There's all sorts of other things you can do if you want/need, such as live weather and traffic, tyre pressure monitor even plug an action cam in and view it on the screen if that floats your boat!
Sure if all you need is A to B navigation then any mobile phone will do. Though I went away for the weekend in the car and used my phone for nav rather than sticking a Garmin on the wind screen. When in deepest Herefordshire with no phone signals I had no maps or navigation, wasn't my best moment - just ask my wife
