I have never done any serious dirt biking (unless you call a little adventuring on the '10 on some dirt trails serious dirt biking), but it is something I definitely want to do in the next couple years.
I have however done a lot of riding in the rain. I wouldn't necessarily recommend that anyone just jump on a bike and in the rain, but through those experiences (one experience had me 6+ hours in down pour rain on hwy 1 from Santa Barbara to San Jose) I have gotten really comfortable with the back end sliding out.
I definitely concur that being able to understand where the traction is, and how much you have left, is infinitely invaluable when it comes to panic situations. But it is definitely something you glean from experience, and no amount of skill can make up for that (imo). I still think that dirt riding would provide another level to this. Just sharing my street experiences!