If you can learn to understand the fundamentals of a given market you can make informed investment decisions. 

You don't need to know everything to get started; you need a foundation to build on, and the rest will come through experience and then refining your education.You can build a basic understanding of investing in 3-6 months.

Start by deepening your understanding of CRE fundamentals, including net operating income (NOI), cap rates, and lease structures like triple net (NNN).

My understanding is that the ballpark standard of "unless it would be outrageously tough" (something along those lines) is what applies if you're doing a rehab, seeking new permits, doing structural changes anyways, and things of that nature.For existing pre-ADA structures, my understanding is that the standard is more along the lines of "if it can be easily/cheaply done, you have to do it."

I don't understand why you've owned an investment for 27 years and only cash flow $600 a month.

There's no precise figure because no one will understand your STR or market as well as you do- or, as well as you will (with time).

I am hoping to learn more about how investors analyze their deals and make decisions, as well as looking to better understand general real estate investing.

You don't need to know everything to get started; you need a foundation to build on, and the rest will come through experience and then refining your education.You can build a basic understanding of investing in 3-6 months.

I'm trying to understand how frequent this is.  

I don’t understand how this isn’t a clear-cut case.