I love a clean interior, but only clean it about once a month.
I use the Carlack plastic care -
http://www.cleanyourcar.co.uk/interior/carlack-68-plastic-care/prod_353.html
As the product is made in Germany i think it suits the German car plastics, none of that cockpit shine stuff which makes the car look taccy.
This just cleans and preserves the plastic, doesnt make it shiney, shiney doesnt suit the VAG plastics.
It makes the dash look like new!
If i want to go all out though i'd shampoo the seats with Auto Glym interior shampoo. Spray on, aggetate with a brush, scrub with a cloth, then hoover over.
Then i'd clean the mats in the footwell, for this i use Chemical guys fabric clean.
http://www.cleanyourcar.co.uk/interior/chemical-guys-fabric-clean/prod_342.html
This stuff is brilliant, i had superb results with it. I squirted some into a bucket, filled with warm/hot water, then used a strong bristled hand brush and scrubbed at the mats. After that i dried/picked up dirt with a microfibre towel, hoovered the mats and then left to dry. They were absolutely gleaming!
I'd reccomend doing this after winter or when its not so wet/muddy otherwise you'd be back to square one in no time!