Whilst it is hard to disagree with you, Rav, in so far as physical existence is the only state of affairs with which we are familiar
I am of the firm belief that anything that is not nothing must be physical because it must have substance. If something doesn't have substance how can one say that it is anything? All you need to do in order to appreciate this is to take any conceivable reality, compare it to nothing, and think about what's different. Something (no matter how abstract or seemingly unphysical it might be) will always be different from nothing in the sense that something is "there", but nothing is not. If something is "there" then how can it not be a "substance" of sorts? All we need to do is embrace more sophisticated notions of physicality which science has already taught us is necessary anyway.
surely this simply begs the question of existence and provides no answer to it.
The answer is, as far as I am concerned, that something exists because nothing is an impossibility. As I alluded to earlier, I believe that presupposing an either-or scenario (I did this myself for many years) is an error which stems from our natural tendency to think of everything as a thing. You don't have to look very far to find people trying to describe or quantify nothing somehow (a vacuum, a void, the pure emptiness that the universe is expanding into etc) but it's all hopelessly incorrect and ultimately futile. It's not useful (or logical) to try to understand what nothing "is". Instead we simply need to understand everything that nothing is "not". All that should be left in ones mind after doing this is a "marker" of some sort that serves to remind you that nothing can't (and shouldn't be) conceptualized at all so you don't fall back into the trap of thinking of it as something.
Again, if nothing is an impossibility, then something must exist, always. And because nothing can not exist anywhere, ever, something must exist everywhere, forever. This doesn't mean that the universe as we know it didn't have a beginning, only that there could never have been a time when all of it's fundamental constituent elements (including the ones we don't know about, yet) weren't somewhere (still everywhere in fact), in one form or another.
I know this all sounds highly speculative (and I'm obliged to concede that it is) but it all flows naturally from the simplest and most logical idea: that nothing is an impossibility. I'd like to see anyone demonstrate otherwise. Honestly I would. I've got the soul of a scientist in the sense that I love to be wrong about stuff like this because then there's something new to explore.