Mirror Image does nothing against: PSI, AoE and burst fire eats it up like a fat kid eats candy in an unsupervised candy store. Robots are essentially ignoring it. No idea what you mean with the idea that you will have so much PSI that you will use it rarely is a massive hyperbole. Even endgame unless you finish every fight in two rounds you will run into rounds where you have to wait a round or two until PSI Booster is off CD.
It really doesn't happen anymore. I played at release, and then, yes, quite often I'd have to hide until booster CD came back.
With the expansion and so many new goodies it just doesn't happen. I didn't have to use a single accelerator or a PSI food yet, and I'm playing Psychosis. The biggest culprit is LTI + the PSI booster CD nerf, the spirit potions help.
MI trivializes stalkers and snipers, you have other solutions for PSI (LoC) or AoE. It's still something others don't get.
If I were doing a PSI build now, I'd probably go full tin can, since the 10% cost reduction from psi beetle carapace is superfluous now.