1 Watching that first video, the overwhelming thing I felt was how VULNERABLE he seemed without the bodywork.  It was scary seeing him come close to the walls and barriers.

I guess the cost/benefit ratio of the technology wasn't good enough for it to catch on.  Or else F1 decided it was unfair and made a rule against it.

2 F1 changed the rules and said "4 tires, no more, no less."

3 Also, about vulnerability: the body work doesn't offer any substantial protection. It's all about streamlining.

4 Mauser, it's strange, but the biggest problem with the long-term viability of the P34-type design had nothing to do with the chassis itself.  Oh, to be sure, the FIA changed the rules to state that a F1 car can only have four wheels, and that put an end to that, but that took six years to occur, in 1983!

No, what killed the P34 as a racer were the tires.  Goodyear had to make each set of 10" front tires by hand specifically for Tyrrell only.  Of course, every other car on the grid could use conventional-sized front tires, so that process was much easier.  Goodyear didn't develop the tire design at all, which meant that in 1977, the P34's second year of racing, it wasn't nearly as good as it had been the previous season, when it had 10 podiums and one race victory between the two cars (17 race season, but it didn't compete in the first three races).

In fact, in the race it won (Sweden, 1976), the P34 finished 1-2.  The following year, there were four podiums total, no wins, and the car was in all 17 races.  It also became fragile, though F1 cars notoriously were in that time.

5 I imagine a thin layer of fiberglass isn't all that much protection, but riding around without it just took away the illusion of protection.

I recall a few Road and Track type magazine articles about other 6-wheeled cars, with the other two up front.  But the car I'm thinking of seemed to have them just to support the load of an enormous engine.

6 Mauser, would that have been the Covini C6W?  Because, strangely enough, all the other F1 cars that had six wheels had four wheels at the rear: the Williams FW08b was the one that caused the FIA to finally create the 4-wheel rule; the March 2-4-0 was a four-wheel-drive car... with all four powered wheels at the back; even Ferrari tried something with the 312 T6, with four wheels on the rear axle...

7 Hmmm, no, this was much longer ago, and more sedan-like.  Fortunately, the commenters on another article on that site led me to the "Panther 6" which might be it.