I've been running at half power (50w) for a long time now. Mainly to save on tubes and I can't really hear much difference between the two. Yes rebias. Yes cut ohms in half. Yes save on tubes. There are advantages of 100w too but I see that as more headroom and more 'girth' as mentioned but these amp have plenty of girth at all wattages. Hell - have you heard some of these 22w 6V6 versions?
I have my bass = 9:30, mids = 1pm, treble = 7:30am ('0'), vol = 11am, gain = 1pm, loop vol = 4pm, Gear 2, OD 2, boosted w Koko or Bad Monkey