On the German Auto Magazine Show (DW TV ~ "Deutsche Welle" Program Name; Drive It) I saw a few cleaning tips;
1) how they used white Toothpaste (needs to be pure white) and a tooth brush to clean the wheels with a tooth brush then using Margarine with a cloth applied a fine coat then polish the end result. I have to make a test one day ... normally they give good tips.
The cost difference of course (well known cleaning products verses magazine and /or clear white toothpaste) is very high so if it works not a bad idea.
2) They also talked about bugs how they do accumulate on long trips. To reduce this the treated the front bumper with "Baby Feuchttücher" = Baby Wipes doing so the bugs did not stick as much to the front bumper and after a 800 KM test run the amount of bugs wea reduced by 2/3 also cleaning of the bugs was much easier.
3) They pointed out how windshield wipers sometimes leave behind streaks to eliminate that they used a "Weichspüler" = softener to treat the rubber of the wipers. This did a fantastic job to remove the streaks.
4) A final tip was to remove rust (not required on our M3's
however may be on our older cars from time to time during detailing. They showed how using Coke and aluminum foil would do the trick. Using some aluminum foil they crumbled a piece and used it as a cloth poring some coke over it gently rubbed the rusted surface. This removed the rust. Then using a wax one could restore the affected area. Not 100% however better looking then before.
Just passing along the tips for everyone.
PS. You can watch the DW TV Programs on your computer the car program is presented in German Name; "Das Motor Magazine" and in English Name; "Drive it" In general cars are discussed also each show has segments that are quite interesting at times, normally near the end of the 1/2 hour program. Links are easy to find just Google it. Apart from the weekly car program they have other interesting Travel Programs like "Discover Germany" should you plan a ED sometime in the future.