That and some of the *most powerful* PrC abilities come from classes that lose caster levels, but belong to casters.
None are ever worth the lost of caster levels except under very specific circumstances, but let's look at the various options.
There's a number of options in Heroes of Horror and BoED and BoVD that progress casting at half progression, while offering all kinds of truly fun spells (at will charm spells, greatly boosted familiars, stuff like that).
The Prestige Paladin class variant. Half casting. All the cool paladin tricks. It's a totally worthwhile 1 level dip for *any* cleric- since at the first level, you lose nothing of value and gain a few extra skill options and a better BAB and HD, and often worth taking to 3 (since it progresses casting each odd level), since lvl 2 is when it gets all the best paladin features. It's probably not truly worth the caster level, but it's still very tempting and often worth it for easy access to certain other PrCs.
Done your way, well, now you have what is effectively a paladin with full cleric casting. How's *THAT* for power increase?
Walker in the Waste (sandstorm) is a scary-powerful prestige class that is only mitigated by the lack of full casting progression. In the right (admittedly limited) situations, it's actually MORE powerful than a full caster would be.
There's a handful of the Drow and other Underdark PrCs that I can't be bothered to look for that are similarly godlike in their environs, and legitimately worth the caster loss if that's where your campaign is solely where your campaign will be held. Now they get to be full casters as well? Heh.
Actually, know what? All the regional books have at least one environmental partial casting PrC that's arguably worth the loss normally, but is absolutely ungodly if given back the rest of their progression.
EDIT: The only case you can make for this "granting more to mundanes" is scenarios which turn said mundane into a caster.
And... uh... well, if that's the argument you want to make, I can't dispute it. A wizard doesn't really gain a whole lot by being remade into a cleric. Some, yes, but not a whole lot. A fighter gains just about everything by being remade into a cleric.