The 2nd gen pistols, especially the later ones, have more in common internally with 3rd gen pistols than what most people realize, so I wouldn't classify them as "obsolete".
Novel? Yes
Heavy? Just a bit ( 41 oz. versus 38-39 oz. for a 5909)
I have a 459 and a 559, the thickness of the grip frame is my main dislike, but not enough to make me want to get rid of them... I bought them after my 3rd gens while in a bit of a nostalgic mood.
A 459 was my first semi-auto pistol (purchased new in 1983) and I sold it a year later after catching the .45acp bug and wanting a Colt Gold Cup in the worst way. I've been wanting to have a 2nd Gen pistol again so I picked up an adjustable sight 559 that was in my LGS display case when I went in to pick up a 4516-1 that came out of the CA 10 day waiting period. A nickeled 459 identical to the one I got rid of came up for sale on another forum a few months ago and I snapped that one up too.
I think had it been the other way around and I still had the 2nd Gen pistol when the 3rd Gens came out, I probably would only have bought a 3rd gen initially to have a .40 cal pistol, and not so much as them being that much superior.
But I also freely admit too... I am a 3rd Gen junkie.
As others have said... if the price is right, buy it... shoot it and enjoy it for what it represents, a bit of S&W history, as you would with an older S&W revolver.