The only reason people wouldn't jump at playing clerics is because they still believe in old misconceptions about the cleric and what it can/should do.
After all, if everyone played a cleric, each of them would only really have to bother with a healing spell once in a while, and they'd spend most of their time blasting, buffing themselves up with spells, smashing baddies with ease, and still having enough magic left afterward to solve some of the town's problems and mysteries, like some kind of troubleshooting handyman/detective/exorcist/jack-of-nearly-all-trades.
Anyway, this really would make wizards weep. Suddenly they're the only people who have to prepare their spells, and on top of that they have to purchase most of their new spells just to be useful for more than just one or two things (i.e. blasting with fire and detecting hidden stuff; if they want more than just 2 spells per level, they have to pay through the nose to get it).
Not only does the wizard have no significant mundane combat ability (unlike the cleric, who surpasses the bard and rogue in most situations; although rogues can do better if they get to flank enemies; of course, several kinds of enemy are immune to sneak attack anyway), but the wizard also has almost zero survivability and only marginally better spell variety (IF he pays through the nose to get it, that is).
Divine casters are already the most powerful and versatile characters around. Versatility does count for something. Anyone who whines about playing a cleric in 3rd Edition is a fool. The best characters I've seen have been clerics and druids (whether playing them, playing beside them, or DMing for them; I've done all three). Making the divine casters even more versatile just hurts the arcane casters more, and, while it may not impact the warriors that much, it will still make the divine casters outshine them more often.
Divine casters have plenty of spells to buff up their own combat ability or that of allies (but especially their own!), plus they have all kinds of utility spells. The cleric or druid will be doing all kinds of neat and useful stuff outside of combat, and even if they expend all of their spells on such activities, they'll still be a solid support warrior if a battle crops up. The fighter, barbarian, or paladin, meanwhile, will be lucky if they can find much to do outside of combat, because they have piddly skill points and class skill selection, and because they lack the caster's general utility spells.
With a Bear's Endurance the cleric can fight alongside the party's fighter without dropping first, and with a combination of Divine Favor, Bull's Strength, and Greater Magic Weapon, the cleric will be hitting stuff just as often and just as hard, if not moreso. With Entropic Shield, Shield of Faith, Protection From Evil, and Magic Vestment, the cleric will have better AC than the fighter, too. And much better Will saves. What the cleric lacks in bonus feats, he or she makes up for with Turning/Rebuking ability and with their many spells.
Basically, what it comes down to is that you should either beef up other characters to compensate for this added flexibility of divine casters, or you should weaken divine casters in some other way to compensate. I know that spontaneous casting makes sense for divine casters, but that doesn't mean it's fair to everyone else; the divine casters are only undesirable to play if the player is a fool or just has a strong preference for arcane or roguish characters. Divine casters are strong enough as it is, no need to hedge out other character archetypes even more. I'd suggest either giving other classes 2 more skill points per level (except for rangers and barbarians perhaps, as they're already fairly strong and versatile compared to similar classes), or reducing the cleric and druid to d6 hit dice and poor Fortitude saves. Paladins already have such limited and focused spellcasting ability, that the change to spontaneous casting would hardly affect them one bit; so if the first option were taken, it would be good to give them the extra skill points too.