for a start it could have been a loose wire shorting out, its not as though things melt for no reason, like why would one melt and the rest be fine??
these things were designed in japan and driven there for 15 odd years with no problems. they come here, which is a colder climate and all of a sudden the cover is keeping to much heat in.... yeah i see where your all coming from.

only part of the coilpack system ive seen fail was on an SR20 and it was the amplifier that failed as it was hanging low behind the block and taking in alot more heat than it was designed for.
thier like everything you look after it then it'll always work.