You are not a collector, so disregard the advice about pinned barrel and recessed cylinder. You'll never care about those small features in a practical sidearm, and if those Hogue grips don't fit your hand, you can easily buy some that do.
Frankly, I prefer rubber grips on most "using" sidearms. They fit my hand better than S&W wooden target stocks and give less perceived recoil effect and are bump/scar proof and weatherproof.
Never mind which barrel lengths some collectors or re-sellers think are preferable. Will this barrel length fit YOUR perceived needs for this gun? As a target arm or for backpacking/trail gun, it's ideal, and many cops have carried six-inch barrels by preference; they're easier to shoot well than shorter guns.
I've owned this basic model in 2.5, four, and six-inch barrels, and each was best for a specific need. A six-inch gun is fine for home defense or hunting small game. Some use the .357 for deer at reasonable range. You should become a master shooter before doing that, however.
Assuming that this gun is in proper condition, as with buying ANY used gun, I'd be on that deal like sweet on honey!
With aftermarket grips and no box, figure on maybe $450 trade value. I doubt you'd get it for less, if the seller realizes what he has. If he's some young jerk raised on Glocks, you may slip one past him and get a deal...
Now, if you live somewhere like the south side of Chicago or in Miami, and your concern is a gun to deal with a gang, yeah, get polymer or a nicer SIG, Beretta, or CZ pistol in 9mm and some spare magazines.
But if you're a sportsman or average guy homeowner concerned about burglars or a snake or cougar in the outdoors, that .357 that will also fire all .38 Special ammo is an ideal all-round handgun.
You'll want something smaller if licensed to carry concealed, but this M-66-2 would remain your basic gun for practice and outdoor use.
If you wear openly in a high-riding holster, the longer barrel won't likely be an issue. You can sit on a log or in a car with a gun that size and not feel discomfort. This assumes that you aren't a short guy, though.
No kidding: If you can lay hands on that gun and it's as it should be, no cracked forcing cone, bad cylinder timing, etc., go after it. Never mind a factory box. You'll probably buy a nice zippered gun case for it, anyway.
The only real caveat is that this size of .357 isn't intended for full time use with full Magnum loads. The very man who conceived the gun told me that he thought it should be relegated to firing .357 ammo maybe 10-15% of the time, when the added power is needed. The .357 Magnum is not "range ammo." It is KILLING ammo, for when you need to stop something evil needing that power. And avoid hot loads with bullets of 125 grains or less: they're very abusive to the gun. Use 140-158 grain bullets, jacketed. Plain lead .357 bullets lead the bore badly. You should be satisfied with a 158 grain bullet at 1200-1300 feet per second in a .357. That's a savage killer on a human-sized target. If you feel that you need more, buy a .44 Magnum. But it and the ammo will cost more and kick a whole lot more. The gun will be bigger and heavier. Short of bears, don't bother.
With the original S&W wood grips in good shape and with its original factory box, I'd say more like $699. 
