I'd say you did pretty well. I believe without the NSW serial number, it is not a navy frame... but I wouldn't worry about whether the internals are coated or not unless you're planning on going swimming in the ocean with it.
I'd say that's not a bad price. You could send it in to Sig for the refresher package. They'll put brand new Sig Light night sights on it and replace the springs and whatnot while giving it a full once over to make sure it's all in good shape. I forget the cost but it's basically the cost of night sights... a little over a hundred bucks I think.
Shoot that thing! Also, the Hogue G10's as seen in my pic are spectacular and make a big difference in the way the gun feels. All depends on how much you wanna put into your gun.
On my MK25, I did the SRT, the Gray Guns P-SPIT trigger(like $50 or $60 and AMAZING), the SRT kit, and the Hogue G10's. It's a kinda pricey gun now, but it's also the favorite gun I've ever owned.
The action isn't quite as smooth as my P229, so I've been thinking about sending the gun to Bruce to have it all smoothed out and put the proverbial cherry on top of my baby.