I won't win any popularity contests for this.
The point about Manuevers is that there are low level Manuevers that are good at all levels. This is what spell casting should do without having the 1/2 class progression. Having 1 level of wizard should give you spells that you want to cast all throughout your career, just like 1 level of warblade. So should 5, 10 and 15 levels. 9th level spells and increased caster level are the rewards for sticking it to the end, but losing them should be as easy as losing the fighter 20 capstone in favor for a 1 level dip into Barbarian.
In the end, I think it ends up with spells. Rework the spells, not the mechanics, to make dipping into wizard or dipping out less painful, and make a Wizard 16/Fighter 4 as viable as Fighter 16/Wizard 4.
tl;dr Its the spells
Right. You're right but...
I posed this same argument when they first started redoing spells...
... everyone hates grease, or was hating on grease at the time, which every other form of it after the original has failed, and made it soemthing no one would cast because why?
Uncomfortability with a low level power spell.
Funny thing is the push was to reign in spell casters, but I think that at low levels when they're a hit away from death they didn't need to be reigned in "generally speaking" and that there are spells that are good at level 1 and good at level 20 grease being the one that springs to mind though and spell that has a decent effect of.
Save or bad ... and bad anyway fits the description.
I think if goes back to the original assertion from the begining, Spellcasters generally dont' have to be redone so much as thier spells need to be redone.
So... maybe multiclassing should come after Spellcaster 20 has been "Rebalanced" on thing I keep saying initially is
"Don't nerf Low level spells" because that makes starting at level 1 for a caster suboptimal as all hell.
Most people who show up on the board or you meet IRL have no idea about how to run a wizard.... they're busily scraping through until they learn some "Real MAgic" aka firebal in that world view.