Reusing yeast from high gravity fermentations is not recommended, it's been stressed. Don't reuse yeast from beers 1.070 and up, as a guide. so harvesting from your Doppelbock is out, so are those from any RIS, Old Ales, Barleywines, Quads, etc.I have two stouts and a doppelbock with S-04 ready to be kegged.
So if I wash these yeasts, make a starter, should I only use them on like beer wort?
You really don't need to 'wash' yeast (rinse, actually). You can pitch directly from the harvested cake, about 1/5 - 1/4 worth.
Don't repitch from very hoppy or very dark beers into much more subtle or lighter styles, generally. Now washing can remove a lot of color, hop debris, trub, etc. but you need to count on making a starter with whatever clean yeast was harvested that way, a lot of good yeast remains in the trub. I've successfully filtered trubby yeast through a piece of voile.
Needless to say, utter care with sanitation is mandatory or you'll grow infections along with the yeast.