Steve,
My $0.02. I have an el-cheapo Chinavasion 7" GPS currently. It's cheap, but as you've found out, ultimately annoying.
When I replace it, I'll be getting something like the Hema Navigator or VMS Touring. Reason being, they're dedicated devices and I expect them to do a much better job than a multi-use device. I just want something I can use, without needing to muck around with it.
I believe the Hema app for the iPad is very good, but I've never used it. I have been considering it also, but don't want to mount the big iPad in the car (and can't afford a second iPad mini). To confirm what the other guys have said:
* The app comes with all the maps, so you don't need to use your data connection when you're out and about. This avoids those telstra bills.
* You will need the 3G iPad or iPad mini - these include a GPS chip. The base-model iPads can't do GPS. You do *NOT* need a SIM card in it if you don't want to.
I'm sick of using my GPS as a rear-view camera - I'll be getting a proper dedicated rear-view screen at some stage.
I think you'd be pretty right with either the Hema Nav/VMS Touring units, or the Hema app on an iPad mini.
Good luck!
Matto