I suppose Sakuracon certainly is big compared to other anime conventions, but not as far as conventions in general go. It' has something like 1/3 the attendance of PAX? I'd consider that a big convention. It's all relative though. For instance, some people would consider Portland a "big" city, and others would consider it "small". For me, the fact that Sakuracon seems to be almost entirely a PNW convention, not a convention that generates a whole lot of national draw, is what makes the difference. Again though, it's a matter of opinion, really.
On subject more specifically, I wouldn't make a goal of making Kumoricon larger, or busier. My goals are actually pretty focused on communication, which is why I've chosen to become to closely involved on these forums. If the communication is excellent, then the experience is vastly improved. It's harder to communicate effectively if you add more people, so I prefer smaller numbers.