Should you buy another Power Stage, new or used if that's your question?
It's like Pagda said one is as good as another if they both work.

My question is did you ever check for power at the coil terminals with a meter or even a test light with the ignition switch on?

You can test the coil manually.
There are two ways to do this.
This will depend on how comfortable you are with different methods.

You can apply power to the coil "directly from the battery" and it should create a spark when you take the grounding lead off the negative side of the coil each and every time.

Pull both connections off and get your self two wires.
One goes to the positive side of the battery over to the terminal (15) +. It was the only terminal that had only one wire on it. It should have a plastic insulator on it too.

The other side marked with a numeral (1) is the negative. This was the place where a tachometer or power stage hooks.
You will take your other wire and connect one end to a ground and touch the number 1 to that grounded wire.
This will cause current to flow through the coil. When you take the wire off that terminal a spark should jump out of the long distributor wire that you have about one-quarter inch away from a strut tower stud and nut. If it does the coil is good. If not its bad.

This is the SECOND METHOD of which, might be simpler, does not rule out the cars other wiring issues like above.
You need to find out the same thing above but with the key "on" in the second position.
You will need only to have the number (15) + terminal hooked up on the coil from the cars original wiring. Take all the others off number (1)- side.
Now ground the coil as before and it should still spark everytime you remove the grounding wire because now you are powering the coil from the cars battery through the ignition switch.

Between the to methods you should be able to isolate the problem from the ignition switch giving power or the ICU and the Power Stage operational side. You have the gremlin contained so its
One or the Other not working.

A lot of this shade tree mechcanic shifting of the wires could be stopped if you had a voltmeter.
They are cheap and simple to use, please get one. The 21st century demands it!
It's a lot easier to back probe those pins and know what you have, how much or where and when.

I have always taught and demonstrated to apprentices that, in most cases, there are two ways to do a job! Even though, there maybe one of them a slighly better than the other, it all boils down too ... "Just as long as we get good results after the efforts of either, Good parts or something fixed!"

Have at it. Figure it out or throw money and parts at it. Lessons learned cost something, it just depends on how you wish to pay for them.
Personally, I have kept my finger tips in my hair and not so much in my wallet. Over the years I think I would have gone hairless, on the back of my head, during the aging process anyway!
(:-)

Good luck!
Phil