Only a problem if you can reliably get all of those materials every time you play. This is why I suggested making the most commonly occurring materials non-magical.
If you have that many materials, getting one or two commons is not unbalancing. Most materials are rare anyway, and most spells will be unused or undiscovered, so the chance that a "create gold" spell ends up requiring cat skin, gabbro, plump helmets, etc. is nihil.
What you're aiming for here is the semblance of "originality" without anyone having to have any original ideas. This doesn't work unless your audience is extremely stupid.
As I said, random materials are mostly a stopgap until someone finds the time to edit them.
Fantasy games also tend to use the "cliche", if that's what you want to call it, of dwarves: short, muscular, bearded dudes who dig in the earth and drink a lot and hoard treasure and make wondrous things out of stone and metal. As we've seen, it's still possible to build something pretty interesting using that as a foundation. On the other hand, if you start by throwing it out and Mad Libbing up a new fantasy race that's (height) and (build) and (facial feature) and builds (habitation) in the (environment) and (recreational activity), then you can't really tell any durable stories about them. You can't build a world this way. The enjoyment of it is pretty much limited to the Mad Libs level of chuckling over the incongruous thing you've created and then forgetting about it.
I agree that a completely randomized world is not fun: that's what the fixed rules are for (you can have so many of them that the random part is negligible). That way a place to summon would have a recognizable setup, but the actual implementation and the furnishings would vary from world to world, and within a world, depending on the creature the wizard specialized in.
As for the concept of summoning, I've just taken a traditional spell example: make a creature appear and bind it to your will. Depending on the cosmology there might be a plane of gibbons, or you're just creating a body for a gibbon soul to inhabit in exchange for its servitude, or it's a kind of teleporting abduction, etc.
Pick one and stick with it, then. Cosmology matters. You can't set up a magic system in which "how the universe is constructed" is one of the variables.
I disagree, you don't need to know the whole cosmology to write interesting stories. Look at the history of the HFS: people invented all kinds of explanations for it... but Toady never had one except a vague notion of "fiery hell full of demons below". Often the event comes first and the rationalization/explanation comes later. And then we can build upon it. But again, messing with the fixed rules will have the most profound impact, because they impact much more than individual spells.
We can derive a lot from general categories - sphere associations, for example, but the sphere associations too have to come from somewhere. So ultimately we'll have to allow a random element somewhere, if we are to have variation at all. And I'd prefer a little wider scope than a random pick between various colours of moonstone to associate with the moon...
I would say that there are some places you could work on something similar to what Silverionmox is talking about, but with a greater control and structure.
For example, you might make a fireball spell randomly select something from a material category, like a "flammable" selection of coke, coal, wool, sulphur, saltpetre, or other things I'm not thinking of at the moment that's an easily flammable material that is already in the game.
To do this, of course, you'd need to give some algorithmic categories to different material types, but that might be necessary in the long run, anyway, just to make things like alchemy work.
Ignition point is a material property that's defined in the raws, it would be perfectly feasible to randomly select one with a low ignition point. Using those values rather than particular materials has the advantage of flexibility when new materials are added.