When a character starts as a priest, there are three options for when to class change:
1. Change at level 9, but then you'd miss out on MADI, which is important.
2. Change at level 11, which is enough to learn MADI (if not right away, after leveling up in the new class).
3. Wait until level 13, to get the final level of priest spells.

The thing is, those last two levels take a lot of XP, when I could instead be leveling up in the new class (which, let's assume, is not Bishop or Lord), and I am not sure if that last level of spells is worth it.

In terms of level 7 priest spells, we have:
* KADORTO, which restores a character from the ash (or dead) condition. The problem is that it still has the risks and drawbacks of resurrection spells, and a failure means the character is lost forever (unless I have something like a (used) Coin of Power handy, but even that destroys the character's class). If a character has turned to ash, I would much rather use MAHAMAN (level loss is easier to deal with than risking death), and for the one Wizardry scenario where that's not an option, I can use a Bishop to glitch the character's condition to "AFRAID", which is easily recovered from.
* MALIKTO, which is nice (hits all enemies), but TILTOWAIT (level 7 mage) is better. In addition, since there are only two level 7 priest spells, a former priest will only get 2 casts of this spell between rests (assuming KADORTO isn't used). Since TILTOWAIT is clearly better, I am thinking that it makes sense to skip this spell level, especially if I am changing the character into a mage.

Any thoughts? Is it worth going to the trouble to get level 7 priest spells, or are they best skipped?

My priest already has two spells (DIOS and BADIOS) on character creation, and level 2 doesn't give me a new spell level, so there's no reason to change at level 2, as once one spell of a level is learned, the others can be learned by leveling up in any class. Also, I find that low level spells are not that useful later in the game, and learning the low level spells before class change won't help with learning the higher level spells later (you have to start back at level 1 after each class change, regardless of your former level, and level is what you need to learn higher level spells).

Also, there's no concept of "magic training" in these early Wizardry games.

The problem with level 7 spells on a Bishop is that those spells aren't learned until level 25 for mage spells and level 28 for priest spells; the game can be easily beaten by these levels. Furthermore, it takes a few levels after that for them to get more level 7 spell points than a former caster would have. (Honestly, why are Bishops so lousy in most* Wizardry games? They really feel a lot like Thieves; a class that is good for one non-combat use (identifying items in the Bishop case), and utterly useless in other cases.)

Also what do you mean "set | return portal" spells? Why would I need them when I can teleport to arbitrary spots in the dungeon with a single MALOR (which is a level 7 *mage* spell, not a priest spell)?

* Most, of course, does not include Wizardry 8, where Bishops are *finally* worth using for once.

(In case you couldn't tell, I am not talking about the Dark Savant trilogy (Wizardry 6-8) in this topic; I am actually talking about the earliest games in the series.)