A D&D world capped at 12th level (and 6th level spells)

[Yora]

All the editions of D&D that I know have spells ranging from 1st to 9th level, with the highest level of spells becoming available at 17th class level. However, a great number of retroclones only seem to go up to 12th or 14th level, removing the most powerful spells from the game.

The E6 variant for 3rd Edition sets the character level limit at 6th, and many people agree that the greatest difference to the regular game lies in spells of 4th to 9th level not being available, at least not normally.

Now, not every setting has really put a great focus on the things that could be done with high level spells and how their availability affects the world. But compared to a world in which 8th and 9th level spells are available to kings, archmages, and high priests, how much different would be a world in which spells of 7th to 9th level do not exist and 6th level spells are the maximum? It shouldn't be as dramatic a difference as in E6, as a lot of really big game changers are 5th level spells, but I'm still curious what the differences would be?

You don't get Resurrection and Greater Resurrection, which already can make quite a big difference. Raise Dead does exist, but that one requires a mostly intact body, and it would be relatively easy to just remove the head or heart of a corpse and destroy it to make raising impossible.
Other spells of 7th level and above that could have some impact are antimagic field, astral projection, gate, greater teleport, teleportation circle, simulacrum, limited wish, wish, shapechange, ethereal jaunt, and etherealness.
Does not seem a significant difference, but maybe some others have more to add.

[Talar]

Looking at the spell compendium wizards just lose some cool spells, not spells that really break the system over its knee. Druids lose master earth(their teleport spell essentially). Holy Word and company are gone as well, which would stop some caster level shenanigans. Greater Plane Shift is also gone, so casters cannot arrive exactly where they want to on other planes of existence that might have some effect. Besides the ones Yora already mentioned I do not see many spells that missing would have a huge effect on things overall.

[ReaderAt2046]

I think the biggest difference would be the loss of wish, miracle, and greater teleport, because teleportation magic is the single biggest game-breaker in 3.5.
With only regular teleport available, and caster level capped at 12, teleport is somewhat more limited and much riskier (always a chance of mishaps or landing on the wrong side of the continent).

[Jay R]

You've started down the path to re-inventing original D&D. Spells above 6th level, and the higher level characters, were introduced in the first supplement, Greyhawk.

[DigoDragon]

The party can certainly manage without those top tier spells. There's some good spells they can still use to own the battlefield, but they have less access to an instant win button. Those high end teleporting spells were always a headache of mine when dealing with powerful PCs who are too lazy to walk through a dungeon.