I've used plenty of self checkout lanes too and it's roughly the same satisfaction as going in a cashier lane. It's still X + Y steps where X is the number of items you have an Y is payment related steps.
(It's possible that I just hate lines (and self checkout?) way more than other people)
Not at all. It seems like a tiny, infinitesimal even, improvement over self checkout. Waiting in line is annoying, spending a minute or two scanning groceries is not. At least in my area, self checkout moves fast enough that I rarely have to wait for one to be available.
No, not really. It's more convenient and faster, sure, but it's not an incredibly significant sort of thing. And the cost/benefit ratio of it (considering the privacy implications) is nowhere near favorable enough for this to seem attractive to me.
There are random spot checks of course, but I don't think this would work elsewhere, not with the high level of citizen trust that there is here. I'm sure they lose some money to people enticed by easier stealing, but the flow of people is so much faster that it's probably worth it many times over.