Anybody tried these?
They claim a gain of 5 - 7hp?
Will it make our rich running engine burn fuel more efficiently? (just a guess..)

I don't think you get anywhere near that kind of gain! Maybe 1hp. I would think Mazda made them just fine.

don't waste your money.

Have a look at the spark plug wires. They are 1-2 ft. long and go basically straight from the coils to the plugs (not buried under lots of other things like previous rotaries). I don't think you can do anything with these wires other than make them prettier.