If I had a larger kitchen, I'd have a dishwasher, though it wouldn't be top of the list to occupy additional counter space. I use the kettle for kitchen hot water, around 2.5 min @3kw, so 5p for the full 1.7ltr. I tend to batch cook, so a cooking day will take 3 kettles, a non cooking day 1, though I might skip a day or two midweek.
I can see how a large family washing up three times a day might save a few quid, for me it'd take decades to pay for itself, if ever.