I use the same equivalent income that would have been spent on a high end restoration to buy more machines.
In many cases, we are talking between $4-10K per machine, if you want a true HEP.
You can buy a LOT more machines, anywhere between 6-8 EMs, or 4 SS machines with that amount of money.
Keep in mind as well that the money spent on the HEP can greatly outprice the value of the machine itself, and may take years or even decades to accrue any sort of equivalent value, so don't expect to "flip" the game for the equivalency. The secondary market is already slowing down due to a number of factors.
However, if this is your "holy grail", go for it, as that is not the point anyway.

"A person can fulfill any dream if they have a plan. This includes hobbies like pinball. Why spend money and pay others when you can just do the work yourself?"

I prefer to know I did the job.
Anybody can do it, if they are willing to embrace restoration and not in a rush.
The other benefit is you learn about the title and know its' nuances.

In reference to any restoration:
"Do it well or don't do it all all."

There are too many examples of work that looks like machines were colored with crayon in kindergarten.

A poor restoration effort makes a game worth significantly less.

This is why many vintage pinball machines are best left in their original untouched state, beyond restoring proper functionality.

"Upgrade to private storage."

Easier than finding another example of a quality machine title.
Many collectors rotate their lineups periodically.
It really works and it is like Christmas all over again.