[Perfectlap]

actually claying is your biggest ally...

there is the soft clay like Sonus Green and the traditional clay. Polutants dull your clear coat so the base layer doesn't shine as bright. done properly (lots of lubrication) there is little damage to the clear coat and you maintain the shine.
Claying with the soft compound won't strip your wax. The over the counter clays are harder and are intened for a deeper clean.


Your biggest enemy with black is washing and excessive detailing. Its a double whammy. Errors are magnified and the results don't last because..its black!
Unless you are sporting the Boxster for a special occasion I would not touch it between washes. If you do decide to shine it up make sure each panel is wet with a detailing spray or some other form of lubrication. Dampen the towel as well.
Basically never touch dark dry paint with a dry towel.

My suggestion is to try using a waterless wash like Optimum No Rinse, Detailers Pride or Poorboys. I would use the traditonal wash only when the car gets really really filthy. When you do use a traditional car wash soap remove the nozzle and blot dry after flooding the surface to sheet off the water. Blot dry remaining beads or puddles, never wipe. Avoid using paste waxes or polishes more than once a month, try sticking to the spray form of any product, it will cut down on the rubbing of the paint. Also get the best quality towels you can buy, I like the Poorboys with silk binding, Poorboys waffle weaves for drying and a dedicated buffing towel when the car is CLEAN.

Being careful in the washing and drying is the key to making the clear coat last.
Personally I would follow up with Poorboys Natty's Blue(once a month) and top that with FK 425 spray wipe to ward off dust build up, a barrier of sorts. That's it.