I thought I read somewhere in the M-T's literature that the output tubes are the only ones actually heating up in the amp and therefore prone to last somewhat less than all the others.  So maybe the JJ rectifier issues are indeed isolated and a quality control issue only.

BTW, today I can confirm that in my listening room, with the gear just bearly starting to break-in, the speakers sound much better, to my ears at least, when they face straightforwardly (i.e., no toe-in).  There's better stereo separation and more soundstage (although at this early stage soundstage is not a strong point yet).  There's also better frequency separation and detailing, as well as a more natural sound.

The described speakers' orientation demand a relatively higher volume setting to get the same SPL 'sensation' as compared to the traditional toed-in orientation, though.  BTW, I'm keeping the equilateral triangle principle unaffected (I hereby correct part of an earlier statement of mine in this regard), as it is only the orientation I'm changing.  My mistake.