Thank you all !!!
I had a successful afternoon removing the Dashboard.
First of all, the rear view mirror snapped off just as described. The attachment is sort of like the snap on a coat, only heavier-duty.
Now for the dashboard. Here's some info in case there are others out there who wish to remove the dashboard. I used a set of pliers on the two middle attachments, since the wingnuts were too tight to turn by hand at first and were a long reach up under the dash. The fasteners were easier to reach once the rubber ducts were loosened from the heater box. The two outboard dashboard screws were obviously very easy to remove. The dashboard was then free to move rearward a bit.
Next, the tach and speedo cables had to be disconnected. The shrouded bezels are easily underscrewed from the bottom and removed. The gages are held in with two screws. The tach could be pulled out far enough to unscrew the cable and unplug the wires (I labelled all the wires for easy reinstallation). The speedo wouldn't pull back enough to get my hand behind it. I had to unclip the speedo cable from a clip next to the brake booster to give a little more "slack" in the cable. Now the backside of the speedo could be reached. I would recommend removing the speedo and tach before unbolting the dashboard.
Next, the main wire harness for the dashboard can be unplugged from the body harness. An interesting thing, however, was that the warning lights were not part of this arrangement. They all popped out of their locations in the dashboard and were dangling!! They all look alike, so I will have fun trying to figure out which one goes where. Fortunately, the wire colors are all different, so a wiring diagram should shed some light (no pun intended). There was no connector to unhook these from the body harness -- they were hard-wired. I had to unplug some individual connectors on the dash and leave this group of lights on the car for now. Chalk this one up to Italian "character", I guess. What's even funnier is that these are the same warning lights that have no labels on the dash! You have to get out your Owner's Manual to understand if you have low oil pressure or if the car is merely trying to tell you that your parking lamps are turned on!!! I would recommend that you remove these lights from the dashboard before taking out the dashboard. This way, each light can be labelled for reinstallation. I may install a gang connector to help reassembly.
Overall, removing the dashboard is not very difficult, just a little time consuming. As I disassemble my Spider, I have been labelling every wire and bagging all the fasteners so that things are relatively easy when it's time to reassemble.
Thanks again for the information.