Actually it should be case-insensitive, at least for US-ASCII (basic English) characters, and it was in my tests...
So please let me know if you're seeing it work otherwise.
One more thing:
The actual matching of messages to event triggers happens once per mail check, a folder or an account.
This means that if there are 10 new messages, and 5 of them match some trigger's conditions, only one event will be generated (for the newest message).
Pent and I discussed how to generate multiple events for this case, he has some ideas, but it has to go into Tasker itself, and he left it for post-4.4.