To be fair, I'm fairly certain there were a lot of stories that Takahashi had originally intended to write within Ranma 1/2. But then, while writing up the individual bits and pieces the whole thing got away from her.
See Doctor Tofu. A heck of a lot more could have been done with the character, but he became irrelevant once Cologne showed up. After all, the only really interesting things about him by that point were:
1: His destructive crush on Kasumi.
2: Um, his profession?
I mean, Akane had dropped her crush on the guy pretty early on. It was a fairly interesting plot point, but almost nothing was really done with it. I feel that, honestly, it would have been very possible for other things to be done with the guy. But alas, he faded away as his relevance was consumed by the ever growing cast. As the story became less "these two can't get along, but are developing crushes on each other" to "harem" his point of existance just disappeared.