I've had them long enough to keep pushing up rents so that I am at the top of my niche, but know not to exceed it because I'm just about at the point where if I raised rents another $50-$100 I'd be crossing over into the lower end for larger units.

This is the most unique real estate investor club, education, networking and mastermind event in the US!

You aren't offering any unique amenities.

This opportunity doesn’t occur frequently but it takes these attributes to take advantage when they do.3 - Blind luck - do enough deals, the unique opportunity tends to present itself.  

No kidding.. each Jurisdiction is unique..

A specialized commercial broker in a specific niche or any commercial broker?

Mentioning unique perks like 'Game Room,' 'Lake View,' or 'Pet-Friendly' can really draw people in.

Any unique challenges?

Those that are portfolio lenders will often develop a niche, where they are really good.

I ask because most who write similar posts on BiggerPockets are unable and I am sorry but  "A unique blend of benefits that are favorable for R.E investors who are sole proprietors" sounds like something a  fear mongering asset protection company will tell you before upselling the expensive and unnecessary asset protection product.