Using longer lines to get more power is not something new even could sound strange for you... Racers and speed-racers have been using longer lines for so long, so you could get some info in racing specific forums:
kiteforum.com/viewtopic.php?f=159&t=2370103 There is a lot of experience using longer lines, and there is an specific IKA limitation rule for lines lenght for racing (as there is for boards width, fins lenghts, etc). Why having a limitation for racing official competitions if there is no advantage using longer lines?
Could be strange first time you try and has nothing to see with kite stability. The kite could be less responsive (slower response/turning) and you could need some practice to get any advantage. If you are using a slow turning kite just think that it wil turn even slower, but anything else... Riding in low wind needs some different technique.
I would only recommend you to use longer lines to get a better low end when using big kites in low wind (when you couldn't get it changing to a bigger board or bigger kite).
My recommendation: just try, try, try... and decide by your own