black is indeed very hard to maintain.there r 2 types of finishes that people like.
1) clean and shiney
for this,, get a formula one cleaner, clean all the stains on the dashboard first and then spray little bit 3CF/7CF shiner spray on the dashboard and wipe if throughly.this will leave a parmanent shiney surface.make sure u dont spray too much shiner as it wud be hard to wipe it and dirt wud stick.
i like this one but theres one problem, during day time driving, the glare from sun hinders ur view.u can leave the area in front of the driver and polish the rest of the dashboard to minimize this.
2) clean and dry
simple dont spray the 3CF shiner on the dashboard.it wud stay clean but dry.
theres an in-between way too, after cleaning the stains, spray some shiner on a cloth and rub that cloth on the dashboard.this way, the shine wud be minimum but the dull look wud go away.