[Supervinnie40]

After applying dressing you might wanna give it a little wipe down after a few minutes. It now has this weird, uneven gloss (looks really greasy and sticky...). Besides, if it's matte you won't see the dirt on it as quickly.

Like has been said; several products can already help you a lot. Special APC for the car will make very light work of most of the dirt you'll find. Spray it on, rub it around with a (clean) paintbrush and wipe it off. Those things can't catch on fire.
For really bad areas you could use brake-cleaner.
But to simply answer the question: using a steam cleaner is fine as long as you use it with a bit of care. Don't use it for a long time on plugs and connectors obviously. But other parts are fine is you wanna clean it that way.