Like the topic says… what do I need to expect when I install 8.0.7 (freshly downloaded)?
Do I need to uninstall my existing copy then install the new?
What about updating the existing drawings?
Both versions can coexist.
You don’t need to upgrade any projects, but if you edit them in 8, you will be forced to update the project if you save it.
I think the only problem can be with libraries, but I’m not sure of details as I don’t use KiCad libraries.
The problem I expect is that V8 has its libraries while V7 its. As symbol and footprint copy is in schematic/PCB file they will open correctly. I don’t know if these saved in schematic/PCB files symbols/footprints have a full path to their source or are based on some variable that can now point to different libraries. Depending on this you can (or can not) expect in some cases complains on them being different than in library.
In the end, it was a fairly straightforward migration.
I got all my schematics opened / saved (and the handful of boards too) to the new version.
The most time-consuming part was having to refresh every. single. power. symbol.
I only had to revert one symbol back to my custom library (4528 - the ‘power unit’ breaks the standard set for the 74xx / 4xxx power units), and migrate two symbols into my custom library (AC plug and AC receptacle - I assume because they are US-specific standard and not worldwide).
Also ran into a couple annoyances with the Windows version I put on my PC at work (Win11, unfortunately) - the grid is very light, almost invisible, and moving a selection with the arrow keys takes FOREVER.
You only have to update as many times as there are distinct power symbols in the schematic. Select one, then Tools > Update Symbols from Library then choose Update symbols matching value. For instance you can update all the GND symbols in one go.
But wait! You can actually update multiple symbols in one go. In my experiment I used Ctrl Left Mouse Button to select +5V, GND and PWR_FLAG, then chose Update selected symbols. All three got updated. So you only have to do one update per schematic, provided you spot all the power symbols in your schematic.
The multiple selection mechanism is very powerful and it’s always worthwhile to see an action from the menus or context menu can be applied to the selection.
should have been “…symbol. type”. 
I did notice the "all of _ " option - I meant that some boards I transcribed had for example, +2.5, +5, +12, +15, -12, AND ground. I’ll remember the Ctrl+left mouse next time!
Would be nice if there was a ‘master list’ somewhere of all the symbols so I can see if any symbols I had in my personal library were in a library I chose to omit (for speed - most all the symbols I use are in a mere ~35 libraries, not counting my personal library).
Tools > Edit Symbol Library Links?
That was how I narrowed down the list of libraries to keep available, as many of the existing libraries I’ll never need, as they are applications I don’t expect to ever use, and which appear to be minute variations on a theme anyway…
Without having to browse each library in the symbol dialog, was there any way to list what is in each library? I was mainly curious to see if any of the symbols I’d created were now in the standard libraries? No biggie, I’ll stay the course, and for the purpose of this thread title, I am satisfied with the upgrade (at least on the Mac; i need to gather a bit more info before I ask questions relating to the Windows version).