Customizing and making your own keyblade would be stupid, it ruins the whole special-ness of having a keyblade and getting Keychains from differnet people and experiances. It'd be idiotic jsut going around and you collect peices to make some mishapen retarded keyblade
Now leveling up your keyblade, that's the idea I like. Similar to how you leveled up your Drive Forms, the more you use a Keyblae, the more it levels up and perhaps you could put skill points in certain status areas
Like, you could up how much strength it adds, or how much magic it increases, or how much MP it increases, or how fast you swing it, or how powerful a single blow is, or even add new abilities to it
And they wouldn't have to make up any cheesey thing, because it makes perfect sense that the more you use a specific form of the keyblade, the more you get used to it, and the more you gain experiance with fighting with it, or learning new ways to utilize it
So the idea of being able to level up your keyblades the more you use them is a totally awesome idea, or atleast I think so