It depends on how you feel about the focal lengths. I had 35L first (2008) and loved it. Then I came across a really cheap 50L and liked its rendering even more, but always needed to bring something wider, so I bought 24LII. After a year I got tired of carrying two lenses and always wishing I had something between, so in early 2010 I started using 35L again. It was such a relief and I still feel that way. 24 and 50 are sold.
What I'm trying to say that if you're really into 35mm focal length like me you won't be happy trying to replace it with a 24 + 50mm.
Optically I found 35L and 24LII to be very similar. The 24 is slightly better, but both are very, very good, so in my opinion that's no reason for picking one over the other.