In this country bigger is always better, but I am not so sure. Even as I am trying to figure out worship and fellowship outside of institutional church, I still wonder why most churches are locked into a "church growth" model. Why do churches feel like they have to grow? When is enough enough? Why can't there just be many small churches, each building true community within itself? Is it our capitalist society that does it? Try and find many companies that say, "No thanks - we're big enough!" They're out there, but they're precious few. Since many people have remarked that modern American churches are built on the "corporate" model (including being in fact, corporations) I could see this being a valid explanation. Or maybe it's simply competitive gaming - "Our church is bigger than yours" is akin to saying "We scored more than you in the Convertolympics".
Sure, there are economies of scale but I am suspicious of using that as an answer since we're not called upon to build efficient
factories churches that take unwashed heathen in by the pallet at the loading dock and extrude sparkling new Christians out the baptistery. In fact, any "economics" involved should be more those of microeconomics, hearkening back to the roots of the word "economics":
The term economics comes from the Greek for oikos (house) and nomos (custom or law), hence "rules of the house(hold)."
When one thinks of the first century "churches", which were basically extended households, we can see how "economics" in that sense could apply to intimate gatherings worshiping the Lord. But ultimately we are called to be in community, in fellowship, and frankly, I don't see how you can be "in fellowship" with a large group of people. There is a limit above which "the numbers just don't work". I wonder if that boundary is somewhere near Dunbar's number? It is an estimate of the "cognitive limit to the number of individuals with whom any one person can maintain stable social relationships"and is estimated to be approximately 150 (with some researchers thinking it may extend up to 300 - but not more than that).
For a funny but definitely NSFW (and also not safe for uptight people who don't like the gratuitous use of naughty words to make a point) explanation of Dunbar's number, see this two page essay about the "monkeysphere" by David Wong. Go give it a read (if you're not an uptight person who doesn't like the gratuitous use of naughty words to make a point). When you're done laughing, I think you'll agree there's something there to think about. And if we want to try to build anything beyond the size of Dunbar's number, Wong's T.R.Y. points at the end of the essay are probably a good start. But ultimately I think "church" should probably be below Dunbar's number, and when it is reached maybe it is time to start a new church?
And while you're at it and I'm feeling provocative, you may want to read David Wong's 10 Things Christians and Atheists Can (And Must) Agree On. It has been around the blogoverse before, but it's still a good read - at least if you believe in rational discourse with people with whom you disagree.
[And extra points to anyone who gets the really bad pun embedded in the monkeysphere essay and posts it as a comment here first.]