I appreciate the help you were in fact able to provide Olly, thank you.
I managed to find the location of stored SMS on the memory card. They are in E:\Private\1000484b\Mail2
I believe this directory also holds all other messaging data including email, though I'm not entirely sure of that. By manually copying the contents of that directory back and forth between the computer, SD card, and phone memory, I was able to restore all text messages from before the reset.
However, this is where it gets interesting. It appears definite that in my case the stored messaging data is what was in fact causing the error to occur with the Notes application. As soon as I restored those messages, the problem re-occured. I then removed them, and the problem disappeared again.
I even went so far as to test it by having both locations (phone memory and card) contain valid SMS data, with one location containing the old stuff and the other just a new message or two received since the reset. I then went into message settings and switched back and forth several times between using each location as the default. When I selected the one with the old stuff, Notes would stop working instantly. I'd then change the location, and Notes would work fine. Back and forth, back and forth, the results kept repeating every time.
And this was even without resetting or even turning the phone off and on. Just switching SMS storage locations from the settings menu was enough to change the behaviour of Notes, every single time reliably. Something in my messaging folders was obviously corrupting things, though I don't know why. Manually deleting all messages still didn't help things.. somehow that message "container" still held corrupt data of some sort.
Anyway, that's that explanation for now. Maybe it will help someone else somwhere down the line. Incidentally, as a side result I also discovered that if you pick the memory card as your storage location for SMS, it will take much longer to load up the "new text message" screen directly from the standby screen. Around five seconds or so, as compared with under one second if the phone's memory is used instead.