My original motivation was to give him more down/chill-time, and he's completely getting that. But unexpectedly, I think he's overall been acting more responsible too -- he puts his lunch away and washes his hands when he gets home without me having to repeat it 100 times, because I'm not even there! And, he's mostly getting his homework done on his own too, without being bugged (by me) or distracted (by siblings).
The really best thing is that I get so much more time with him now. After the other two have gone upstairs for bath, Gabriel hangs with me while I clean up the kitchen and make lunches. Tonight, he wanted to see if a movie for a book his class is reading ("Island of the Blue Dolphin") was available, so I told him we'd look it up after kitchen chores were done. So he loaded and started the dishwasher, wiped the table, and took out the garbage, while I made lunch and we chatted. Actually it was really Dave whose workload he was reducing, but I totally enjoyed being with him -- something I'd never get in the bad old days of the "you get 15 minutes to eat dinner, then you have to get back to your homework" struggle.
I don't mean it's all perfect, and Gabriel is still unmatched when it comes to digging his heels in (though he has a close rival in his sister, whose latest rude habit is to refuse to listen by putting her fingers in her hears and glaring at you while she wiggles her tongue back and forth taunting "biddle-biddle-biddle!" sounds)....but on the whole, I'm totally reaping the benefits of his extra time. And my initial objective has been met: he's quite a bit calmer, and, well, happier.
And bonus -- we save over $300 a month in childcare, tax-free! It's like someone's paying us for a happier child?!