Here is an interesting deal that I thought I should pass on. Dreamhost is offering Dreampress (combined VPS + db server… much like what you have now) but they’re offering the combined deal for $20pm (intro. offer) for one site (your hosting site).
It works out about 33% cheaper than to do it the traditional way of hosting plus two servers. No idea if it is rock solid, but based on our experience, it should be pretty good. It looks like it might be a good solution for a growing website.