I had my car fully machine corrected when I got her, see the link:-
http://z4-forum.com/forum/viewtopic.php?f=11&t=20526&p=290878#p290878
She stayed in more or less that condition through careful washing for 6 months, unfortunately I then had a crash and the bodyshop got their hands on her, then in the week after that the dealers washed her by mistake (they don't take that much care) so she has quite a few swirls now and will need re-polishing to get totally perfect again.
It depends where you go and what you want doing as to how much you'll pay, you can get a basic machine correction done for £250 upwards, DetailingWorld is one of the best places to check out potential places to go.
If you want to keep the car looking great then you could do worse than to do the following
*Pre-rinse the car with a high pressure hose to remove muck, ideally using snowfoam.
*Use a good quality microfibre wash mitt or similar to clean the bodywork, one bucket with shampoo water, one bucket of water to rinse it in after every couple of passes across the bodywork.
*Dry the car using a good clean drying towel
Basically, in my opinion it's worth doing, although if you have the patience, then you could buy the equipment you need and do it yourself for the cost of doing it once at a Detailing company. (I've done this and will be machining it myself from now on). With basic care the finish can be maintained for quite a long time, my dad's car is still more or less perfect a year after he bought it.
