Games : Does increasing your Insight unlock new items to buy from the Insight Bath Messenger?

In Bloodborne, I had 11 Insight and have about 12 Madman's Knowledge. I got 2 stolen by an enemy (I guess), so now I have 9 Insight.

The Insight Bath Messenger has obviously now disappeared, since I dropped below 10. But when it was available, the only things I could purchase were:

At 15 Insight, the difficulty increases.

So if I use up all of my Madman's Knowledge now, I'd be at approx. 21 Insight. Would that then make any new stuff available for purchase at the Insight Bath Messenger; to deplete my Insight level back down below 15?

Because I don't see a reason to keep a high Insight level; therefore I'm just stocking up on Madman's Knowledge atm.