Originally Posted by Thomas Anderson

What are you on? If you assume 24ish songs each night, you have to count those hits out of both nights, so that takes you down to 32 immediately anyway!

Looking at recent setlists anyway I'd assume the basic setlist each night to include...

Livin' On A Prayer
You Give Love A Bad Name
Lost Highway
Born To Be My Baby
Captain Crash And The Beauty Queen From Mars
I'll Sleep When I'm Dead
It's My Life
I'll Be There For You/These Days (Richie)
Have A Nice Day
Who Says You Can't Go Home
Keep The Faith
Bad Medicine ~ Shout
Wanted Dead Or Alive

So immediately you're looking at 13 songs, so that's 26 gone out of your possible 48, taking you down to 22. As you say they could do a further 2 or 3 new songs each night, taking it down to maybe 16 - but realistically the chance of getting 16 rare tracks is damn near impossible. I did a count on the shows that I went to over here (Manchester and both Twickenham) and found a basic set of 17 songs across each show, and then in Manchester we got 9 extra songs, then Twickenham 5 and 7. Of those extra songs there were a few good rarities - Diamond Ring, Dry County, Blood Money, I Believe - but a couple weren't so big, and in the US they don't seem to vary it so much. Obviously I hope that you do get good shows, but I think you're over-thinking it.