I find old roguelike source codes interesting, because I started from C-style myself and then went to C++ which is in many ways better than C and that's stating the obvious. Back then however C++ didn't even exist or it was new to people. In a way it still is today and some people are unaware of its benefits.
Still, there is something great in those old C source codes. It's the way authors forced the game to emerge from that chaos. Despite of number of dangers from using raw arrays and global data. Whereas today authors are much more engine-oriented like myself. However engines are bad as games and sometimes writing a game engine can take surprisingly long time.
That in mind I have really changed my strategy especially in Kaduria and it seems to work. I no longer try to create a "perfect" engine but try to look at how to implement features as fast as possible, while trying to use the game engine's building blocks in the process.
