I worked hard to increase my earnings.

If you have no desire to sling a roller or a hammer, get a job as an Admin in an PM company.

All that makes the property less desirable for a buyer buying your property when you eventually sell off.Developers typically have maybe a 9 cap or so in it and sell for a 6 cap and lose maybe 100 basis points to real estate commissions, short term capital gains, etc. so might profit 200 basis points.

Highly desired school district, class B+ neighborhood.

Low range homes often take more work because they tend to be in worse condition and require more inspection visits and tougher negotiations.The difference is she'll earn $1,350 vs $15,000. 

A general valuation formula many in the industry use is: # of economically occupied lots * monthly lot rent * 70% (assuming 30% of income goes to expenses, common for parks on city utilities) * 12 (months in a year) / desired cap rateFor this park at a 10 CAP (many parts go for lower cap rates now, but small parks might still go for a 10 CAP), that makes: 21*298*.7*12/.10 = $526K . 

Class B Single Family Home would be a home in a desirable neighborhood with nice finishes, but not a new construction top of the line home. 

If the US makes it harder for people to immigrate and/or less desirable, it's plausible that immigration will no longer be able to offset our smaller family formations (along with potential labor shortage on certain jobs/trades), and we will become much more dependent on older age citizens, similar to what's happening in Japan.  

And in reality, a Realtor can’t sell a $30,000 house, earn half of an $1800 commission, and stay in the business.

In my neck of the woods, the older suburbs are much more desirable to tenants and owners, so are appreciating faster than the suburbs that were built in the late 90s through early 2010s, but this was holding true even pre-pandemic in my area.