S&W began using model numbers in 1957. Model numbers are stamped inside the frame, behind the crane, like this.
The .32 S&W Long, and the guns chambered for it, have a growing group of loyal fans here. I own four myself. Value would be based on the actual condition of said revolver, whether it had the original stocks, box, papers, tools. Your location will have lots to do with value to. $150.00 for a rough shooter grade gun to $400.00+ for a perfect example. Older guns have the serial number stamped or written inside.
The .32 S&W Long is marginal as a self defense cartridge; however, Buffalo Bore and MagTech offer such cartridges. If those are unavailable, a target wad cutter bullet would be a better choice than a lead round nose bullet. These are .38 S&W cartridges, but show the different bullet design. W-W on the left, Buffalo Bore to the right.
The S&W 30 was discontinued in 1976.
The S&W 31 in 1991.
Not rare, just discontinued.