audiomagnate, I agree with mroatman on this one. The brown stuff is the transparent laquer layer that got brown with age and exposure to moisture and sun radiation. Yeah, probably some nicotine too. Cleaning the dial will mean removing that layer from dial surface. That will probably bring out the dial paint color and the hour markings' golden shine. Moisture can eat through the paint to the metal dial surface, usually forming bubbles or spots like the thumb marks on my kirovskie up the page. If there are no corrosion spots you can manage achieving a reasonably clear white dial, but the laquer layer is no more. It has to be done gently as even cotton can leave markings if swiped with force.
Then we come to the printing. Fortunately it's not much on this dial (no hour and minute prints), but this iconic logo has very thin lines, and I can't even guess how it will respond to cleaning. Sometimes in my experiments it gets to the point when the dial is clean, and only the logo and jewel count are swimming in pools of brown. I sit there staring at it, wondering if he whole thing was a mistake from the beginning, but it's too late. Sometimes I'm quite lucky with the print. The print on the kirovskie was exellent, I saved every curve and spot, but 1. it was a $15 watch, and 2. I had a NOS dial (the reason I bought it) waiting to take it's place in it. Sometimes I'm not so lucky, and I wish I kept it in the original brown dirty condition.
Having said all that, I'll be honest with you, I would love getting my hands on this dial. I would pick a very small spot at "made in ussr" and see how it responds. You can use a sharp toothpick to clean the golden hour indentations (dipped slightly in your cleaner of choice). Wood won't scratch the golden surface, but careful not to force a slide and scratch the paint outside it. If you try cleaning them with cotton bud you may overdo the painted area around the markings.
Whatever you decide, I'll be following this with great interest. I wish I could get this dial, but usually everything with vimpel on it comes with a good pricetag.