Most of the PC-98 characters are extremely boring. Save for a few exceptions: Mima, Shinki, Yumeko... and... yeah.
You forgot Rika, who gets 2 stages and is more developed than a lot of Windows characters as a result. Yumemi and Chiyuri also have the single longest dialogue by far of any characters. So, yeah, they're pretty developed by Touhou standards too, except form the playables [Including those in IN] and the focal characters of the mangas.
Yuki and Mai also have quite the dailouge and are unique in Touhou being a duel boss.
Anyway, as a big proponent of love for the PC-98 characters, allow me to explain:
A big thing that is so attractive about them to me at least is exactly the fact that about them are question marks. They are mysterious, and as such, it allows theories to flourish about them, and the characters to be developed.
For example, WHY does Rika dislike Reimu enough to send tanks at her? She dosen't appear to be working for Mima, or after the power of Hakurei like the others in SoEW. I usually go with 'Rika's a mad scientist who hates youkai, and thus Reimu who gets along with them for a human'.
Or 'Why is Yumeko called the 'Doll of Misery'? What is her power where she turns into a green outline and phases around?
Or Elly. Why does she work for Yuuka? Why does she have so many references in her design and even the name of her theme [Seriously look up the meaning and just as importantly the origin of 'Perdition'] to Ankou, a personification of death? And if as that suggests she is a Shinigami of sorts [Both the Ankou and a Shinigami are personifications of death...]; WHY DOES SHE WORK FOR YUUKA?
This is all from someone who would happily put Shinki, Rika and Elly in their Top 10 of characters, Yumemi probobly in the Top 15, and Mai somewhere in the Top 20.
Although, there are some characters who get no love at all. Like Orange and Sara and... who was that samurai in SoEW again? Notable in that most of these have been 'replaced' of sorts [Former two by Meiling, latter by Youmu]. With the exception of Yumeko, who was 'replaced' by Sakuya but is still rather popular in her own right.
Also a lot of people say 'when is there going to be a Christian thingy in Touhou' after the Taoists and Buddhists and Shinto sections. Most of them don't realise that PC-98 had loads and loads and loads of Christianity references.
Specifically:
- Sariel's angelic appearance is like a Christan Angel
- Yumemi's weapons are CROSSES
-
Perdition Crisis
- The land you fight Yuki and Mai is a land of Fire and Ice in Makai, which is the daemon world [Aka: Basically Hell]. A lot of depictions of Hell are both fire and ice. [Dante, anyone?]
- Pandemonium [Shinki's castle]
- Shinki herself is a very strong reference to Lucifer
Makai is always tied with Christian references. Hell, Byakuren was in Makai and what did the fandom nickname her? Youkai
JESUS.
Also despite all this PC-98 love I throw around, I'm not one of those people who keep pineing for the return of characters. In fact I frequently speak against the guys who keep thinking Mima will come back.
PC-98 is an interesting place if you actually dig.