I don't mind cleaning up a really dirty gun. At least if I'm the one who's going to enjoy the gun in the future. Dirty guns are, by definition shooters. They got that way by being shot. Its kind of what they were designed and produced to do. Its very rare to find a gun that is "shot out". And you can tell that condition almost at a glance.
Value questions are hard to answer. There are just too many variables. The big one is your own personal financial position, quickly followed by what other guns you have, and then "how badly do you need this one?" After that is sorted out, you start to run into regional price differences. Some places just seem rich in guns. I live in that kind of place, but don't be confused, prices may even be higher here because there are so many gun nuts chasing them!
And then there are variables in the guns themselves. Mentioned here is an S serial number M29. Those are very sought after and the price seems higher and they don't last long on a gun show table.
Keep in mind the idea that guns are hot sellers these days. Many of us could be said to have enough guns to tide us over for a few years. By any objective measure, the only reason we might buy another is because we want it! And depending on the level of that want, reasonable prices can fly right out the window.
So let my suggest the following. Yes, a M29 with a nice finish, regardless of it being blue or nickel, is generally worth $550 around here, and an easy sale at a gun show. Any S serial M29 will bring $700 around here if its serviceable.