I have an M&P of almost the same age and almost the same condition, complete with the same shabby nickel plating. A little metal polish will help its appearance. Serial # 491xxx would likely have shipped in the late 1924-early 1925 period. To indicate a value, I paid $230 for mine a couple of years ago, which was probably a little too much. But I just liked it, and aside from cosmetics, everything is sound and tight. The grips on yours are at least period-correct and likely original.