Agree with pretty much everything you said here. One other big advantage Killington has over most resorts is that when the conditions suck such after a thaw/freeze, Killington will make the mountain much more fun than SB. I've been to SB a few times after these thaw/freeze events and had sheets of ice, death cookies, and chicken heads. Yeah, ungroomed is great most times, but there are plenty of days in a typical NE season where you need the snow to be tweaked,Pico does have more character than Killington- the one department Killington really lacks and it sucks. The Summit Glades, KA, and Giant Killer to name a few. The old Poma line will scare the crap outta you...I'd argue it's tougher than Rumble at SB but doesn't get the attention as it's technically not a trail.
K woods and SB woods are equal in my opinion, when the snow is equal (as it was this year as Killington got more snow than SB, quite rare). Killington woods do certainly see more traffic though, I would say. But if you go midweek and there's fresh the powder lasts a loooong time in places that are on-the-map but a PITA to get to (Centerpiece, Patsy's, Anarchy, Roundabout glade). But Killington has nothing on Castlerock or Mt. Ellen or Paradise. Just as SB has nothing on Killington after Cinco de Mayo or before Christmas!
My thought has always been, if Killington and SB both got 3 feet of snow and I had to choose a full midweek between the two, I'd choose SB. If I had to do a season pass, it's always going to be K. Peak season SB definitely has superior terrain, but all those days where its "less than peak" Killington will almost always have better options, especially pre-Christmas.
Now that SB is unlimited we will target there as much as possible when the conditions are decent and save the K days for those challenging condition days. We also will hit Stratton on getaway days to take some time off the commute home. This year i ended up buying a K spring pass anyway as i didn't have enough days on the K pass and spring skiing at K is a ton of fun as others have posted. Not as good as pow days, but then the corn is there all day and pow is tracked out pretty quickly.
I skied Killlington Saturday and while conditions are deteriorating as they are everywhere in the NE, I would bet there is much more open and skiable than SB at this point. Friends were there the prior weekend and set it was bleak, and then we had the very warm spell.