The cabinets on my B/W have thicker ply than my Sterns.
The playfields on my LOTR LE and SM are the same thickness. Didn't count the plys though. My SM PF is a little grainy.
IM did feel way flimsier than my SM or LOTR but I haven't had a chance to measure the cab or pf thickness.
I have had no issues with my SM or LOTR when it comes to things working, yet other than the one blown magnet fuse. But they are relatively new.
Stern flippers do hum. Sometimes louder than others. They will fade over time as they are single coil wires. Using the PBL upgraded LOTR coils has pretty much solved the issue on LOTR as they are thicker guage wire and handle the heat better.