This sounds absolutely fantastic. So much fun to be had. Let me try to get my ideas out here...

First things first, my suggestion would be to have the different components all represent different aspects. For instance, perhaps verbal components tend to guide what the basic effect of the spell would be, so you could mix and match different verbal components to get different effects (the elements are easy ones, different types of glamour are, of course, always appreciated, &c). Somatic components control area, range, target and the like. Material components would control intensity.

But, there's always other components to consider, such as a focus, which I would consider to be something that always specifically allows a character to perform more efficiently and powerfully, but only in certain veins of magic, a la the Dresden Files way, where he has a blasting rod that specifically allows him to use fire magic with more finesse. XP is also a valid component, but I would suggest XP work by emulating one of the other slots, allowing a character to burn XP when they need a boost. Not sure any other components are popping to mind at the moment.

Now, specifics: the easiest way I can think of to have the verbal and somatic components to work would be that a verbal component by itself does one thing, and adding somatic components to it allow you to change something related to the specifics of the verbal. So, Ign alone shoots a line of fire for as long as the caster can concentrate, but throwing in some movements could warp that into a orb, maybe just a single target, a cone, or the like. More complex movements might allow you to split the fire, or other fun stuff like that. But, if you wanted something a little different, maybe you throw Ign and Ele together, creating a stream of electrified fire, which can then be modified as normal. Some mixes would be weird, but that could be figured out later.

Material components would be, like I said, for effectiveness. Like, the Ign by itself only really deals an amount equal to your caster level every round. Burn up a match while you cast the spell will make it 1d4 per caster level. Holding a piece of coal and burning it as a component boosts it up to 1d6, while burning through some gasoline boosts it even higher. Maybe something really impressive, like a red dragon's scale, would maximize it or something.

My suggestion for material components would be to separate the components into designations, something like Least, Lesser, Minor, Moderate, and Major, maybe add a Unique or something like that at the end. Then, specify what each component does for every individual combination of verbal components (meaning, depending on how many you allow, it could be a very long list).

Least components are something easy to obtain, like a match; something you could realistically carry a lot of, but that do provide a benefit. Going further up, the materials would slowly become things that are less easy to find, either because they're just rarer, or because they're more expensive, or maybe dangerous to use? If the component is gasoline, maybe it can explode on you if you don't pace yourself? Something like that.

In the same vein, I would say that anything that is Metamagic related actually be a material component, and that it have specific sort of relations. You want to maximize your fire spell? Go get a red dragon scale. Just enlarge it? Got any fire salts back their, Bernie? And so on.

Foci would be slightly different, but I would essentially make them items you need to craft (or possibly get a hold of, since I assume some people could use other, special foci), but which more or less add a free slot or two (or three) to your spellcasting in certain ways. So, going with a blasting rod, maybe it adds two additional slots to use, for no extra cost, but only when using fire magic. A more general focus might be a staff, which just gives you one extra slot, but to almost anything you could use. Frees up your attention to make the spell more detailed.

Finally, XP acts similarly to a Focus, but it isn't a material object, and therefore can be used whenever. It's a significant cost, being literally your experiences, but when you're out of options... well, you use what you've got. Maybe make it some kind of simple exchange? 500 XP for an additional slot, 700 more for slot number two, or something like that? Hell, maybe just 500 per slot.

I'm sure other components exist, but those are what I came up with on the fly. I love this idea, and I'd love for it to go somewhere. Good luck.