I would think that by "mundane" Franklin means "not that interesting".
I think that anything that answers that 4 criteria is that interesting by default.
Look at the BS in the software patents world.. it almost certainly extends to other fields.
Even if only 100 of them "deserve" patent protection, how do you conclude that all of them will be interesting? And how many people do you think need to find it interesting?
My underlying point is that patents are nothing to be in awe of. Just because it's patented doesn't mean it's interesting. I get the feeling that you want "interesting" to be a requirement of the patent office. If so, how do you define it?