4. Since the upgrade costs the same number of miles as a full Business Saver award, presumably it is always more economically efficient (in total usage of miles plus cash) to go for the award rather than the upgrade.
5. The logical conclusion therefore is that it makes no sense economically to seek an upgrade; a Business Saver award is always better.
Perhaps that's generally true, assuming you can find a saver award. But then even if the total price in cash plus miles were the same for buying Y and upgrading versus buying a J award, there is the modest benefit of the extra miles earned if you buy Y and upgrade. Maybe buying a J award has modest additional benefits too (some chance of an op-up to F (must be rare), maybe more protection against a downgrade (not sure if this is an issue)).
I have gotten supposedly special prices, less than two weeks out, for upgrades on U.S. flights recently, where they cross out the miles required and replace it. This is for an upgrade confirmable at booking, or technically a separate transaction the instant after you book. In these cases the cash outlay for Y was around the same as the taxes and fees for a J award and the miles were the same or fewer for the upgrade. I don't think I have even seen a corresponding "discount" on straight awards, and rarely see saver awards anyway.
Example: I just paid around $1,350 for a flex-plus Y one-way DXB-DFW with an upgrade for 81,900 miles at booking, around a week before the flight. (I looked for the straight award for the same flight, and I think it priced out at 138,000 miles.) The flight earned a paltry 5,000 miles. For the return, I had booked a straight J award (flex-plus) ORD-DXB three months in advance for 138,000 miles and around $850 in taxes and fees. These are, depressingly, both about as good as redemptions get to the U.S. most of the time these days, and I found the upgrade award a slightly better value. Considering the earned miles, it cost around $500 to save 61,000 miles, which is pretty much a wash in my view, but I am on the borderline for requalifying for Gold and don't have any miles expiring soon, so I took it. They also offered a flex Y ticket with instant upgrade on DXB-DFW, for less cash and more miles of course, but I found that a slightly worse value.
Note that these were both for B777 routes, while I would have preferred the A380. I was limiting myself to routes in the Central or Pacific time zones as I was traveling to PHX. (I am really hoping they start flights to PHX/LAS/DEN.) DFW was suboptimal for this trip, as I needed two flights to get to PHX on UA, but I liked the flight timing, leaving DXB at 2:00am arriving 8:00am, instead of a daytime flight like the majority of U.S. outbound itineraries.