Heintz Art Metal Plate; Clean it Up, or Sell As-Is?

5 3/4" diameter, ~5/8" high; 6.5 oz. Sterling on bronze, pre 1930.

Heintz artificially patinated much of his bronze art with a dark brown finish...which is long gone here. Also, the surface of this is slightly matte, an' I don't know whether that is original, or a result of subsequent cleaning. As there are prominent stains, an' some very fine scratching (as if from nylon scrub pads) my inclination is to go 'bright' by using a judicious, gentle application of proprietary techniques that have served me well over the years.
Yes, I know...it is what it is, an' like coins, the universal counsel is to leave it be as it is. At best this item isn't hugely valuable, an' there are folks for whom original or 'as-is' patina isn't as important as for others; those are my intended eBay audience.
As an aside, I cannot locate any information about the keyhole
or mushroom symbol above the pattern number, pic 4. Can any of y'all illuminate that for me?
I value your comments an' suggestions, even if I don't always follow them. As always, thanks for lookin'!

 

I have this piece by them. I contacted this Heintz collector web site., http://www.heintzcollector.com/about.htm. They told me once the finish is altered in any way the piece loses all its value

 

That's lovely, Marie...thanks! I'll check their site out.

One reasonable conclusion would be that, based on its current condition an' appearance, it has already lost 'all' its value...so, might as well go ahead with my plan.
Problem with that is I've no way to say for sure that it has been previously altered...what it looks like to me may be only loss of finish from use an' age, so as 'original' as it could be, given those caveats.
I may just offer it as-is...save myself some effort...an' avoid damaging what may be 'original' finish/patina...the market will decide its value...if any.

 

Maybe @verybrad has some ideas? He has commented about old copper pieces in the past.

 

Unless you have the ability to re-patinate it, I would leave it alone. Someone will want it as-is. It won't bring top dollar but it certainly has not lost all of its value.

 

Agreed, Brad...an' Thanks!