The Local Interfaith Council...of BADASSES!
Obligatory.
World Of Badass - Television Tropes & Idioms
Some of us gather in solemn prayer.

Some of us gather in orgiastic sacrificial rituals.
But NOW we gather to whoop your interdimensional ass back to the Far Realm.
http://tvtropes.org/pmwiki/pmwiki.php/Main/DidYouJustPunchOutCthulhu
Actually, the ALL Evil party reminds me of Necessary Evil, which I enjoyed playing. Perhaps the orders of light went down first, leaving nothing but the bad guys to save the world...so they can take over it.
http://tvtropes.org/pmwiki/pmwiki.php/Main/EvilVersusEvil
Your right, saying "I cast fly and invisibility and I fly over the guards" sound like much more fun than actually planning out and executing a stealth attack or timing their rotations and sneaking past them or stealing some uniforms and posing as guards and bluffing your way through.
The faster you burn through the story the better you are doing right??
I suddenly remember that whole big fat argument on Narrative control and why "Billy gets to build a demiplane".
Frankly, all it means is that flying over the guards invisible is a solution, but the guards are JUST that low on the totem pole, they barely even register as red shirts. You gotta kick things up a notch.
Why
cant the guards fly?
And if this place was worth its salt, why didnt they have a mages guild engineer their security? Or hire a wizard/witch hunter to train their personel to deal with supernatural/magical enhanced attackers-which in a fantasy world are more dangerous than most mundane ones?
The 5 things everyone should worry about when securing any place are:
-Flying (With magic OR wings)
-Invisibility
-Scrying
-Teleportation
-Incorporeality/Etherealness
Oh and that stealing uniforms thing, any Evil Overlord should have figured that out by now if they are genre savvy.
http://tvtropes.org/pmwiki/pmwiki.php/Main/DressingAsTheEnemy
In fact, I KNOW its on the EOL. In any case, as for spending entire sessions planning, I've done it in Shadowrun and Call of Cthulhu.
EDIT: why cant I ever reliably get these links to convert to plain text?