One thing we noticed in the gaming group was how only non-spellcasting classes were the ones that picked up a level here or there of another class except where it might be needed for a prestige class. And we were all of a consensus; it just hurt the class otherwise if you were reliant on your spellcasting. Not only did it stunt your spell casting progression, but also your effectiveness as it changed your caster level. So, I came up with a proposition that has given a little nudge of assistance.
Rather than having a spell rely on the character's effective caster level, we simply have it based off their level. The result? Nothing big, but it does help the classes with limited spellcasting a touch more and makes some multi-classing less reluctant. Let's say you have a 4th Bard who took a fondness of firearms later and switched to Gunslinger for another 6 levels. Even though he's casting as a 10th level character, he's still limited to the three 1st level spells and the lone 2nd level spell. So, it might buff up a Cure Light Wounds and make his Hold Person last a bit longer. But when you consider these are the lone differences in a group of 10th levelers, it's not really that much as the DC stays the same. If anything, it makes that spellcasting of the Bard a bit less wasted and relevant, because they might actually have a chance to use it once in a while instead of feeling like it was a wasted facet of the class.
My group has been playing with this minor change to the rules for almost two years, and it's not ruffled a single feather. Now, if I could only get them to even give a try to my alternate dice rolling system of rolling 2d12 and increasing the DC of everything by +2 instead of a singular d20...
Not a bad idea. There is also the Magic Knack trait that increase your caster level by +2 as long as it doesn't raise your caster level above your total level.