My first answer was mostly just to yank your chain, when I said "does it matter". I think this is a natural curiosity of man, as to what is in our sky, and how far to it extends? Right before our eyes, and not knowing, has sparked the curiosity of man since the beginning of man, and probably to the end if there is one.
It has to be as vast as the grains of sand on the beach, but not sure if figuring it all out is even possible(at least for now), which also begs the question of "does it matter" if we can not even take care of this planet? The biggest answer to that question is that, if there are only hundreds of universes, reaching them is nearly futile, not to mention millions, billions, or an infinite number. At least in all the lifetimes of everyone living now, we can not really reach much further than are adjoining planets in our own universe. That may be very questionable, when we just saw how 5 months in a space station affected men.
Yes it matters because the idea of so many universes makes us ask why, and what others have earths like ours, and maybe most important, nearly no way to reach each other. It will not matter much, if this planet does not get a grip on itself, and stop destroying the only one we have to survive on. We continue to make this one more polluted, more pron to total destruction from mankind, but also to make its ecosystem so out of balance it will die. God placed every living thing on this earth for a reason, and the balance of the food chain, and ecosystem is pretty delicate. If we want it to matter how many universes exist, we need to start living like it matters how we take care of this one.