a friendly warning
Let me just warn everyone, speaking as someone who has extensively used (abused) Mirror Image, that if you go by a strict interpretation which disallows things like targeted spells (magic missile, etc.) to dispel images -- this spell becomes hideously over-the-top great.
Mirror Image is my staple defensive spell. Not as in, I cast it sometimes. But as in, I cast it always. Every battle, at the start, or ahead given a round or ten to buff.
There is no situation where mirror image is bad, or suboptimal.
And it doesn't even have a duration of 1 rnd/level! How crazy is that?
Going against spellcasters? Stop those "save or be screwed" spells entirely! What mage will target you (and 7 of your figments) when they could instead target the scary-looking cleric or fighter?
Going against a big scary melee monster? Step up to the plate. Wade into melee. Monster full attacks. Step back 5', recast the 2nd level spell. Monster full attacks again. Step back, if necessary recast or maybe not if there are 3-4 images left. Etc. All the while your pals are not being attacked and are killing the thing. All you "waste" are a few 2nd level spells.
Going aginst a bunch of monsters? It works great, it stops them from hitting (or getting in a lucky crit) 95% of the time, while you can cast spells or hack away. Usually low-level baddies don't have multiple attacks...
Going against undead? Stops those pesky level drains wonderfully well.
Etc.
There are no, and I mean, no, counters except True Seeing (completely effective and very rare), Whirlwind attack (less rare but still very rare), and... that's it. Done. The only other way is to actually attack each image. This gives a typical caster 2 or so rounds of damage-free, spell-targeted free fun. That's a huge advantage. Of course, if the monsters avoid you because it's obviously hard to hit you.... one Mirror Image easily lasts the whole combat.
Oh - the enemies can close their eyes and attack of course. Giving a 50% miss chance and etc. Seems like a dumb idea. It's never really worked out that well.
As a player, a strict "no magic missile no targeted spells" rules makes my mouth water.
As a GM, it just sucks. It's very boring to play out, and the party will get tired of enemies who are always Mirror Imaged in return.

)


for tat, etc.)
Note: it is a rather dull spell to play out. "ok i hit image 4, is that the real one? No. Ok it's dispelled. Ok I missed the next one I think. What is it's AC again? Uh, 14. Ok I missed it..." etc.
Further note: There are a few other spells that should be looked at in comparison to Mirror Image. Blur (2nd level) simply reeks. Displacement (3rd level) is nearly always worse than MI and lasts a fraction of the time. Etc.
To sum: resist the urge to power up mirror image for the sake of your game. Let magic missile, other targeted spells dispel figments. It's just a 2nd level spell, after all.