Since we, my partners and I, derive all of our income from the rental properties, perhaps that's the reasoning?

It is very difficult if not impossible to derive any type of appreciation from these type of houses.

Mindy,UBIT stand for Unrelated Business Income Tax and applies on any income in your 401k that would derive from active trade or business.

One correlation does not mean causality, especially when using macro data to make prediction of an asset class that mainly derives its value from local conditions. 

@Tom Dunkel hit the head on the nail... if you plan on deriving your offer based on the NOI and you include capex, most likely you'll fall short of what others will be offering.Good luck!

All numbers in the RE listing are suspect and it's your due diligence to find where YOU would at COE + one day.Get the rent-roll to find the current GSI and prove or best estimate of the expenses to then derive your annual NOI. 

@Steven Hamilton II Code § 871(d) and §882(d) allow a foreign corporation or international investor that derives income from real property, but that is not engaged in a US trade or business, to elect to be taxed on a net basis at graduated rates as if the income were ECI.See §871(a) below:(a)When election may be made.

My wife and I are currently disabled and our incomes are derived from being retired.Can we invest in real estate if we live on a fixed income ?

These two do exist solely as lead generation for agents, as their income is derived from selling zip codes for agents to receive buyer calls (ever wonder why they show 3 agents  for a property, and none of them are the listing agent?)

Real estate is an umbrella term for income derived from such asset.