I have posted these reasons for owning an old one before, but will re-post here:
My M41 was purchased by me, brand new in 1979 - paid $430.00 if memory serves. The older models have features that are not to be found on the newer models.
The older models have roll engraved markings vs the new laser printed ones. The older magazines are a thicker, heavier gauge metal and far far superior to the new ones and extra magazines fit perfectly right out of the box - unlike some of the new ones. The grips on the newer models are made of plywood (laminated) whereas the originals are solid Walnut. The bluing on the originals is also far superior IMHO. Fit, finish and slickness out of the box is also better on the older models. I've also noticed that the triggers seem better on the vintage models as well. Even though they can be adjusted slightly by moving the spring in the adjustment notches, the new ones are a bit heavier from what I have experienced with new ones my friends have bought.
Last but not least, the list price on the current crop of M41's is $1,400.00 + tax. Even with a discount, they are more expensive than most used M41's sell for ($900.00 - 1,100.00). Since the basic operation of the new ones is the same as the old ones, internal parts are readily available and S&W will still work on the older models AFAIK.
If you are really lucky you might even find a vintage model 41 (pre 1978 I believe) that has a cocking indicator. Not necessary of course, but kind of neat!! So those are my reasons for a vintage model over a new one.
Oh - I have also noticed that most of the pre-owned vintage model 41's (in particular) have been kept in great shape by their owners. Since they are basically an indoor target pistol they don't seem to get beat up like many other guns do.
NOTE: The S&W M41 is a GREAT and accurate target pistol! That said, you might also consider a vintage High Standard (in various models). They are also GREAT!! Were it not for the Slide Release control being on the "wrong side" of the gun and the Magazine Catch being on the Butt, I'd have bought one myself.