Outside of the Eddie Rips Up the World Tour, I would still argue that the others were not really surprises. '99 was (supposedly) based on fan voting, in 2003 those songs had all been on multiple tours after their respective albums. Those songs you mentioned for the 2008 and 2013 tours were "dusted off" but could be expected based on the premises of the tours. If anything, I was more surprised by how conservative the selections were on those tours, especially after 2005.
My original point was looking forward to 2018 and you'll note in the above list, Maiden seems to be getting LESS adventurous with setlists over the past decade plus. I would love to be surprised, and we can quibble about how rare something like Die With Your Boots On truly is*, but Maiden has shown that roughly 75% of their songs don't have a chance of being played live.
* I really like Boots and think it is quite under-rated. They also happened to play it 2 of the first 4 times I saw them, so for me it isn't that rare. I would count it as a surprise going forward, but would truly be shocked if it appears again.
The return of Bruce and Adrian meant that Maiden were able to bring back from retirement many songs that in 1998 we thought they would never play again.
1999: Aces High and Powerslave are back after a 14 year hiatus. Phantom of the Opera is back after 12 years and Killers after an 11 year absence. Wasted Years and Run to the Hills are back to the setlist after 6 years (it was played at a few shows in 1993).
2002: Children of the Damned is back after 15 years for 3 charity shows. It would also be later played at a few shows in a short leg in 2009 before being welcomed back to the set in 2016 for a world tour.
2003 GMETID tour: Revelations is back after 18 years, 22 Acacia Avenue and Die with your Boots on are back after 12 years, Bring your Daughter to the Slaughter is back after 10 years.
2003 DOD tour: Can I Play with Madness is back after 11 years.
2005: Another Life is back after 24 years, Drifter is back after 22 years, Murders of the Rue Morgue is back after 21 years (7 if you count the few times Blaze butchered the song in 1998), Where Eagles Dare and Remember Tomorrow are back after 12 years.
2008: Rime of the Ancient Mariner is back after 21 years, Moonchild is back after 20 years. Aces High, Powerslave, and Wasted Years are back after 9 years.
2012: Seventh Son of a Seventh Son is back after 24 years, The Prisoner is back after 21 years, Afraid to Shoot Strangers is back after 14 years.
We have also had brave setlists, like the A Matter of Life and Death tour in 2006 or the first leg of The Final Frontier tour in 2010, playing mostly recently released material.
Songs like Children of the Damned and Powerslave have been mentioned because they have not been live staples for quite a long time. The last tour where Children of the Damned was played on all legs was the Somewhere on Tour in 1986/1987! Sure, Powerslave was played in 1999 and 2008/2009, but has not been played live that often compared to 2 Minutes to Midnight or even Aces High.
Could they be more adventurous? Of course they could, but the setlists we get nowadays are a blessing compared to the "5/6 new album songs, 2 songs off the previous album, the same old classics with an encore featuring Running Free and Sanctuary" that were the norm for most of the pre-reunion era. And for that I am grateful.
If they could only play Flight of Icarus again... I have seen Bruce do that when he was solo back in 1997, but it would be great to hear it played by Maiden again.
