Joined: Nov 2006
Posts: 19,810
Likes: 597
From: NJ, NYC, LI
Bikes: 1940s Fothergill, 1959 Allegro Special, 1963? Claud Butler Olympic Sprint, Lambert 'Clubman', 1974 Fuji "the Ace", 1976 Holdsworth 650b conversion rando bike, 1983 Trek 720 tourer, 1984 Counterpoint Opus II, 1993 Basso Gap, 2010 Downtube 8h, and...
It really depends. If your cottered crank is ugly and heavy and you have a better cotterless one in your parts bin and all the parts you need to make the switch, then what the heck, do it. Especially if you're making an upgrade that the manufacturer made within a few years of when your bike was made. Like, what's the harm in making an early 70's Super Course more like a later 70's one?
On the other hand, there are some really nice cottered cranks and it would be sad to upgrade a nice cottered one to a crappy cotterless one. Not that you'd be the first one to do that.