You improve VFR nav through practice. You don't need to do it all the time; 3km vis and being lost near controlled airspace are times when it really isn't a good idea. But sometimes it's great fun flying and being able to see the whole area below you looking just like it does on the map, and it will, with practice. It's a useful skill, it's a lot of fun, and it could stand you in good stead if you ever fly an aircraft without all the fancy stuff. Of course, it's not a great idea in darkest Africa or the High Arctic, but I think we're talking about Britain in summer here, aren't we? So of course radio nav is useful, so is GPS...but so is map and compass nav; where's the conflict?