Those critters are pretty simple devices... I doubt they're to blame by themselves..
I'd be figuring about wiring being bad, or a controller bad..
I floggin hate it when you have a so called tech just swap parts w/o investigating reasoning it happened.. its sorta like a fuse blowing, or pretty much exactly like a fuse blowing in your case.. the fuse or a glow plug doesn't just blow for the helluvit, something putting too much strain on the circuit is what causes it to blow.. that something should be identified instead of just replacing the messenger..
So.. on either side of the plug could be the cause.. the plug could have ignited something which caused it to blow, like oil.. it could then simply burn up, and the aid of voltage allows it to blow up when its ability to dissipate heat is exhausted.. a leaking valve seal could do that.. a good way to check for that (that is non invasive) is with a vacuum gauge.. get one and watch it.. Google for vacuum gauge diagnostics for more help there..
I'd guess the issue is on the other side, though, and related to wiring.. of you're tossing too much voltage at those things, then you've got a problem.. they will burn up just as likely.. check the wiring harness for wear and exposed looms.. be pretty dang thorough around areas where they are adjacent to other wires that carry voltage.. was the controller swapped when the plugs were? If not, I'd ask the dealer why they werent..
Techs at dealers man handle those harnesses.. they get in the way of work, and its easier to push pull or bend them out of the way.. hell, I push pull or bend them out of the way.. that ain't smart, though.. those harnesses are full of tiny not well protected wires, and between that and heat, its easy to bust up the insulation on them..
Grab yourself a multimeter, put that bad bear on continuity checker, lay out your wiring schematic, and start looking for wires that share continuity that ain't 'sposed to.. wiggle and squeeze the harness whilst doing so.. albeit gently..
By the way, I always let my plugs warm too.. I figure tuere is no harm in doing so, and they warm in a coupke seconds anyway..