We had the dealer applied 'diamond brite' ( or whatever ) on our cars ( both a couple of years old from a Honda dealer ) and it has been fine for many, many years, a good shower of rain or a simple garden hose brush and shampoo stick will clean the cars even after 6 years +. So I really never clean our cars and they look fine, still a good depth of shine - I think we paid about £200 for the Jazz to get done ( White Orchid Pearl, a surprisingly pragmatic colour, it hardly shows the dirt ), and on the Civic the dealer threw it in FOC - so in my experience the claims made for the professionally applied nano finishes are true, and not just sales hype. I do use AutoGlym bumper care on exterior plastic like scuttle, along side window seals and roof trims and it still beads up rain after months, and keeps plastic smear free.
I have made a habit of using AutoGlym super resin polish on headlight covers about once a month ( when I think about it ) , and they are still clear as crystal .
Ask 100 people the best way to look after car paint and you will get 100 different answers, many involving expensive potions and arcane methods of application.