I have never used a Munki and I know next to nothing about digital negatives, so I can't really comment about those aspects. The i1 is an impressive piece of kit, and it seems that it does most things very well. Unfortunately the price reflects that. You have to take a deep breath to buy one, but most people who do don't seem to regret it. You have to view it as a long-term investment.
The big advantage of the i1 over the Munki, as I understand it, is that the i1 can measure smaller patches. So you can print profiling charts with more patches on the same amount of paper, or use less paper for the same amount of patches, or some combination. I would not be surprised if the i1 is more accurate, but I don't know whether that's actually the case.
I have written a blog article containing my thoughts on printer selection. I have only very limited experience with Pro printers and none using Piezo. That said, my general advice to people is to take (another) deep breath before moving to a printer with ink lines and dampers for Piezo. But if you already have a 9800, you already know most of that.
I'm not sure what you read, but I haven't said that. I've never seen that error. As you can see, the spreadsheet is locked. You could create your own version. All you really need is the luminosity tab, and it is fairly easy to create your own spreadsheet that does that. The pink line plots your luminosity data as the QTR linearise program spits it out. The black line is just a straight line between the max and the min values, the maths for which is pretty simple.
The density tab is effectively plotting the same data - i.e. it's converting the density data that you enter into luminosity in order to plot it, so it doesn't really add anything. It's just an alternative way of entering the measurement data. Piezo is linear in luminosity. If you were to plot the density version it is a curved line. So if you really have problems, create your own using just the luminosity data, or download a fresh copy of the IJM one.
My advice would be to edit your post to remove your email address to prevent it being harvested by spammers. PMs are a better way to communicate email addresses..