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

In Bloodborne, I had 12 Insight and 12 Madman's Knowledge.

At first the Insight Bath Messenger had for purchase:

I just defeated a boss...

Which I bought, along with a couple of items, to drop me back to 4 Insight.

At 15 Insight, the difficulty increases.

So if I use up all of my Madman's Knowledge now, I'd be at approx. 19 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.

Update: After reaching 15 Insight, I bought all of the stuff I originally didn't want, purely to get me back below 15...

Update 2: After buying some additional crap I don't need, to get the Insight back below 15; my Insight eventually got to 16 again naturally. I've decided against buying any more crap from the 2nd Bath Messenger, and trying out the game at a harder level... maybe it has some benefit? It appears nobody knows.....