I've tinkered around with the 1 meg ohm pots and have them in some guitars right now. the first guitar was picked mainly just to try the pot and had nothing to do with the pickup or the woods but just on the convenience of which guitar didn't have some tripped-out wiring or a p/p pot or anything like that.
the other was based strictly on trying to open up a dull-sounding guitar. turns out this guitar had more issues than the girls working the day shift down at the Jiggle Hut and the pots were one of many steps.
in both instances the pickups are higher output models like a JB or a hybrid made of a JB and a Custom, so as a reference they are not quite as open and clear as the BKP models. but I can say the gave each guitar a bit more headroom. it's not something I was able to hear and immediately think "oh, that's a 1 meg ohm pot!" I think the shift from a 250k to a 500k is much more obvious. however, I do believe that every little thing adds up and if you're looking for a little more 'air' in there, it'd be a step to take. in both instances, I have no need to revert back to 500k.
to bypass pots, are you talking about a blower switch or just unhooking pots from the chain? I have a guitar I've been meaning to wire a blower switch into for about a year and just need to get around to doing it. I've seen where some guys say it's not like night and day, but it's a subtle bump frees up the resistance a bit to help with a little more sparkle when wanted.
you guys can shoot me know, but I just don't use tone pots, so I just unhook them. I leave them in there so there's not an empty hole, so I just call them dummy knobs. this is also one of those things where I can tell that subtle difference where the signal will have a little more 'essence' or 'life'.