HOW USEFUL ARE GPS UNITS REALLY?

I know GPS units are not a toy, but do we really need one for a CSR trip?

Our party have betwen us been to heaps of out of the way destinations, and have generally been comfortable about our navigation performance, ie we have not got lost.

We are going down the Canning Stock route in late August and I have been given the job of investigating / getting the GPS. I have read a good text, talked to lots of sales people and am still not convinced we need one.

If I do get one, I reckon the $400 bushwalkers unit would be enough. The $800 outfits seem to be lots of fun, but the extra features like built in maps and brackets and computer download facilities and more user friendly keyboards seem nice but hardly needed. The accuracy and the info on the cheapie seem the same.

But - do we need any? The enthusiasts among the sales people tell how easy it is to navigate all the time with them - but the big green signs on even minor tracks seem pretty easy to me. When you get to station country and remote area tracks a few odometer readings scribbled on the map seem to give accurate enough waypoints to keep track of where you are. And a silva compass and remembering the old boy scout training seem to tell you which direction you are going ok.

What am I overlooking?

Any user experience in the Canning or anywhere else that can help us decide please?

Thanks

Max