Personally I would always call any aerodrome I'm going to be flying near to let them know who I am, where I am and what I'll be doing. It doesn't have to be a long, rambling call - just something like "Anytown Radio, this is G-****. PA28 from Somewhereville to Otherplace, will be passing 3 miles North West of your aerodrome in 2 minutes at 2500 on the Cotswold; will advise you when clear" Invariably the aerodrome will be glad for the call. Mark you, when I did the same at a small military aerodrome and was told "Do not enter the MATZ", I was somewhat cross. So they were told that we would be passing over the aerodrome at 3001' a.g.l.......but that was a few years ago, I'm a bit less stubborn these days!
The routes I use for PPL Skill Tests involve flight near other aerodromes in Class G airspace as a deliberate test of the pilot's airmanship.