No because once you get to about level +30 the normal enemies don't level much. And abilities are allowed you just can't junction magic to stats.
That's not true. Random enemies keep a level range according to the average level of your three fighting party members. (Most) Bosses, on the other hand, have a fixed upper level, so it's still benefitial to keep high levels. Random encounters can be avoided with Enc.None and such anyway.

One trick though is to keep 2 party members at a very high level and 1 at a very low level. The lower levelled person will bring down the average a lot. You'll have to judge for yourself if this is worth it though...