The first run isn't much fun. There are useful skills in just knowing how to build stuff, and knowing all the constituent parts of a running system. But overall I suspect you'd learn more in a year of using Arch.

But on subsequent play-throughs, you get to be creative! Want to ignore the FHS and try putting your apps somewhere weird? Want to use a different libc or init system? Build everything around an esoteric shell? Go for maximum optimisation? It's the replayability that makes Linux from Scratch fun, and yes, totally worth working out what your own distro might look like.