I just took a closer look at things because the bulging of the case caused by the beeper, which leaves the bottom left corner loose, has continued to bother me.
I am now of the opinion that it is the domes themselves that are inconsistent. This has been mentioned elsewhere by some people including one of the only reports of someone succeeding at fixing their keyboard woes. Pressing on the individual domes carefully and in the center, I can now feel that the keys I find snappier do have snappier domes and vice versa. Why the bottom row in particular should have mushy domes and why there is some consistency in complaints with this row between customers remains a mystery. But, I no longer feel that alignment alone can fix this, and having busted out a ruler, I don't think the alignment is too bad. Now, I'm kind of expecting that with use all of the domes will revert to the feel of the mushier ones, but we'll see. I won't really be disappointed if that happens.
Separately, I found I could get the left side of the ENTER key to be clicky, at the expense of the right side, if I completely loosened that PCB screw. Not an option, but an interesting observation. The bottom line here is that the PCB tension is preloading the left ENTER dome, I'm pretty convinced now. Moreover, this is the same edge of the PCB as the beeper, and it seems to me that the PCB can't be pushed against the housing quite as far on that edge as on the other edge (CLX edge). I wanted to blame the plastic ledge/cliff on the housing immediately behind the LCD, or some component on the dome side of the PCB, but I can't really see any asymmetries with either of these things or anything else. I'm stumped.
There's something funky going on with the ENTER side of the case. I think this is the cause of the ENTER key problems and the bulging induced by the beeper. I'm a little surprised I haven't heard anyone else mention the latter so far. Does anyone else have that problem? In my case, I've now resorted to "fixing" it by putting a small cushion of masking tape on the back side of the PCB behind the EXIT key. Not ideal, but it feels much better now, and I think I'll finally be able to use the machine peacefully going forward
ETA: I initially tried repositioning the beeper a little to see if it could sit in a spot with more room in the metal backing, but this didn't work.