How long will it stay that clean?

Heh. Probably not long. There are plenty of car valet places round here, so even if I'm too lazy to wash it myself (likely), it won't be too hard to keep it clean.

If you are going to wash it occasionally buy some zymol, even if all you do is smell it

That's the stuff that smells of chocolate and things, yes? Frankly, looking at the price, I think all I would be doing is smelling it -- it's far to expensive to actually use on the car.