I've sold properties to investors who hold portfolios and for lack of better word the properties are all trash and then I've dealt with some who have a well-oiled machine.

That may sound pretty good...until you discover that their net worth is decreasing at a rate of $2 million per year, and they've got $100 mil of adjustable rate debt on a portfolio of D class properties that forces them to work 80+ hours per week just to keep the whole thing afloat...Investor B tells you "my net worth is $1 mil" --to many successful investors, that sounds like a relatively insignificant net worth...but, investor B owns a portfolio of A class properties with zero debt, professionally managed, their cashflow is $500k per year, their net worth is increasing at a rate of $1 mil per year, and they only have to work about 1-2 hours per week to keep their machine going.Personally, I'd MUCH rather be investor B than investor A, even though investor A's net worth is 10x of investor B's.So yeah, tracking net worth is advisable, but it's only a small part of what an investor should be tracking and modeling, and net worth alone might not be very indicative of an investor's success.

Bare bones cash-flow machines.

When we remodeled our previous house we put a treadmill and a rowing machine downstairs.

It's also when you're buying that "machine" that someone has put together, there's added value over a practice.  

And the tenants are generally very pleasant to work with.When I worked for a construction equipment manufacturer, we designed a brand new line of skid steer loaders and what we found was that all the profit came from the large machines.

It kind of reminds me of that George Carlin saying "They don't want a population capable of critical thinking, they want obedient workers, people just smart enough to run the machines and just dumb enough to passively accept their situation."

I have used deal machine and propstream before and didn't like them so much.

As far as the copper pipes needing replaced in a few years , well so may the water heater , the furnace , the dishwasher , and washing machine .

@Lenny Machin these guys are right.