Thank you for the report, and I'm sorry to hear about your bad experience. I also had problems with so called mechanics with expensive offices misdiagnosing my Astro, because they did not bother to check the TSB's. They started taking things apart that were not even related to the issue.

Scotty has mentioned before in his videos that he doesn't think much of Windy City mechanics. We have a page here for keeping track of good and bad mechanics, so I'll add your report there. ( https://carkiller.com/scottykilmer/qa/mechanics/)

That being said, misfires have a lot of different causes and they are notoriously difficult to diagnose, and mechanics hate them. If you're a good mechanic equipped with a lot of experience and good tools then you can narrow down the problem quickly. If you're not, then you can spend hours tracking it down and most customers will not want to pay your hourly rate for all that time, especially on older vehicles. If the mechanic eats that time, then the business loses money. So unfortunately there isn't much incentive for a mechanic to spend a lot of time diagnosing, and many will just cross their fingers, replace some parts, and send you on your way because they still get paid.

So did you get your misfire sorted out, or are you still having it? My 2000 Astro had a misfire which was caused by a clogged fuel filter, and an out-of-timing distributor. That was a random misfire though (P0300) and you only have one misfiring cylinder (P0301). Also check out the misfire section of the FAQ and see if that helps. These vans are also notorious for eating intake gaskets, so that might be something else to check. The fuel injection spiders were also updated.

As for the harness you pointed out... it might be concerning but it's not likely to be causing your problem. Even though the wires might look damaged, it didn't look like they were severed. Do you know what the plug you showed does?

Where is your oil leaking from? I had leaky oil cooler lines and it was an easy fix.

I also recommend joining the forum chevygmcvans.com

There is a wealth of information to search, and people there with lots of experience with your van that can help you with this problem and others.

I'm so sorry to hear about this. It's too common a story. 

If there's a lesson that can be learned, as painful as it is, it would be to learn a bit more deeply about the codes and research possible fixes before seeing a mechanic, the better to understand whether a mechanic or shop is trying to hose you.

(As for the oil leak, just drain out the fresh "alien" oil and refill with your PennzOil high mileage. Hopefully, as the PennzOil dilutes  and displaces the foreign chemicals, the leak will get better over time. Sometimes the different additives create undesirable chemical reactions in an old engine. As you get rid of the synthetic blend with your PennzOil, there's a chance the leak would slow or stop). 

In this case, P0301 means (as you can see from the enginecodes link on this site) that cylinder 1 ONLY is misfiring. It does not mean that all cylinders are misfiring (which is a P0300). 

So, the investigation should have started with that cylinder ONLY. That should have been the sole focus of the diagnosis. 

Scotty always says "simple and cheap." 

1. The simplest thing was to assess the ignition coil and spark plug. That was a reasonable assumption, for starters, IMHO.  As has been mentioned by others on this forum, all the mechanic had to do was swap ignition packs between cylinders. Then run the scan tool. 

Let say that you swapped the coils between Cylinders 1 & 2. If the ignition pack that had been in cylinder one was bad, when you ran the scan tool, the error code would have been P0302. If that was the case, then just replace the single ignition pack, and you were good to go. There would have been no immediate need to replace the other three ignition packs.  

It's a very simple diagnostic that either rules the ignition pack either in-or-out. 

2. Spark plug removal is a reasonable next step. Visually inspecting the spark plugs, without previous experience is possible with a visual guide (available all over the Internet, BTW). 

3. You can test for power/ground for the wires. If you see a break, it's relatively easy to fix with a soldering iron and a bit of specialized wrap. (You could check the fuse, as well, to see if it has power and ground).

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4. If it was something related to the "air" part of the air/fuel mixture, there was no harm in properly cleaning the MAF sensor and throttle body. It's good practice, actually. (From what I saw of the receipt, they cleaned, not replaced, the MAF. That's standard practice. But, Scotty has a video on that. It's easy, and cheap for you to do).

It wasn't clear to me that they actually checked for vacuum leaks, in hoses, for example. Nothing in your exposition suggested that they did so. 

5. If it's on the fuel side, a misfire could have been the result of a clogged fuel filter. If you have an external fuel filter, it would have been an easy fix. However, generally, if the fuel filter is clogged, it would affect multiple cylinders (and perhaps throw a P0300 not a P0301).

6. You could have a clogged fuel injector. A clogged injector would trigger a P0301. Scotty has a video on cleaning fuel injectors. You can run the search of the 2700 videos from this site, and find the fuel injector discussion.

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As for the "parts cannon," who knows the quality of the replacement parts? (That's an open question). 

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This isn't an exhaustive list, but it's an example (however imperfect) of how to think through some of possibilities, before you seek out a mechanic. 

Have you reported them to the Better Business Bureau?