I clay my car every spring before giving it a serious wax. I use Bilt Hamber Double Speed Wax.Throughout the summer I wash it every week, using the two bucket method and rinseless wash. Just before autumn sets in I wax the car again, then during the winter months I wash the car as regular as the weather permits, especially if it gets really dirty, taking care to wash the grime of the lower half first.
Regarding petrol, I have tried the V-Power, liked the increased smoothness (maybe all in my head), but couldn't justify the exorbitant price.. I have used supermarket fuel for years now, in a range of cars, and never experienced any detrimental effects.
I record and collate my fuel consumption figures constantly. I recently was given a ScanGauge and that gives me loads of interesting data. I never noticed any increase in mpg using the better fuel, certainly not enough to warrant the extra expense.