There's no way anyone's going to disagree with the current consensus on the worm, so let's take a look at a slightly better high-level monster!
Chronotyryns are Large, and have 17 magical beast RHD, which isn't as good as the outsider HD it could plausibly have had, but still quite nice. Their ability scores are solid across the board, though its extremes are 'only' 26 strength and charisma as opposed to the truly immense stats some other high-level monsters offer.
The birds' chassis is rounded out with SR 31, resistance 20 to a bunch of elements, and an useful 70 ft. fly speed. Less notable are the DR 15/magic and the natural attacks.
Special abilities are varied. Some are quite forgettable, like Sonic Burst (a 1/day AoE that deals modest sonic damage), or Feather Flurry (a 3/day 2d6 natural ranged attack). Others are modest but usable, like at-will Detect Magic and 10 effective ranks in all knowledge skills.
And then there's the truly great abilities, first of them the SLAs. At-will Blink, Feeblemind, and Greater Teleport are certainly useful. 3/day Displacement is a bit underwhelming, but it's more than compensated for by 3/day Time Stop. 1/day Iron Body, Temporal Stasis and Plane Shift are useful, but seem almost underwhelming in comparison. Secondly, they have 12th-level sorcerer casting.
And thirdly (and most importantly), Chronotyryns get two turns of actions per round. Obvious timestop synergy aside, this is completely ridiculous for all the reasons that messing with the action economy is overpowered.
So what to rate this? The obvious point of comparison is a sorcerer, and the chronotyryn stacks up pretty well to one. Sure, losing several caster levels hurts, but getting an entire second turn and some great SLAs (in addition to a much better chassis) makes up for it in my opinion.
Though this beastie is very hard to balance, +2 is probably the best possible level adjustment. That way, it'll be somewhere between tier 2 and 3 in power.