Well, a nighttime study would have to be done. I don't know what the skywave issues might be. But I think you'd be surprised how little practical difference doubling power would make, especially on today's interference-choked AM band. We initially planned to upgrade 1040 to 10kw back in 2003, but then we decided to go for everything we could get with the existing array - no new land or towers, and so 20kw emerged as the plan. But 10 more kw only moved the daytime 5 mv/m out about 10 miles.
Just for laughs we also toyed with going to 50kw daytime, which would have required 2 more towers for a 6-tower array. It would have moved the 5 mv about another 12 miles further into Lake Ontario, doubling the electric bill and costing another $500k vs. the 20kw plan. Since 20kw 4 towers produces 5 mv at the Lake Ontario shore, we left it at that.
I think most listeners would notice little difference were WBEN to go to 10kw. But if they could get FIFTY....
(WTEM in DC went 50kw on 980.....hmmm.)