223 is not a mini 30-06 - 222 is close to a mini 30-06.

All depends on your opinion as to "how much" improvement is required to make it worthwhile. And the improvement is not always equal across the bore diameter of various case designs (people tend to think the 25-06AI is a good improvement and the 30-06AI isn't much of one).

In general, cartridges that use slower powder (25-06) or have more taper (Mauser or 250 Savage based cartridges) will see more improvement. As the bore for a given cartridge case gets bigger, appropriate powders generally get faster, and the difference gets smaller - a 6mmRem AI or 257 Roberts AI = well worth while. A 9.3x57 AI (same case necked up) = not so worthwhile in my opinion. Same goes for the 308 family (no reason in the world to make a 358 Win AI, but folks see good improvement in the 243 AI).

Of course sometimes you might want to do it for improved headspace control (I love my 375-06AI).