It's not just about the materials, it's about taking the time, setting out the ritual space, putting yourself in the right frame of mind, checking your books to see you've aligned the forces right, establishing the symbolic link, that kind of thing. Also, only evocation uses rotes.
Even if you've done the spell before, you still need to check that you are laying everything out right the next time you do it. After all, if you knew enough to do it perfectly without that, your (effective) Lore would be high enough that such preparation would not be necessary.
Just exchange "acquire special materials: +2" for "check special materials are still fresh: +2" and you'll be fine.