Looks like we're going to have some fun with this thread. I've got a few things to contribute in relation to chapter 4 and chapter 21, but I will leave that for another time.
I think we need to be cautious in this enterprise. When it comes to literal versus symbolic, I believe it is a mistake to see everything as either / or. Who knows how much of the Revelation is supposed to be taken as both / and. For instance, the seven churches are certainly literal churches that received the words of the Revelation ca. 100 A.D. However, I believe it is folly to restrict the interpretation to this literal level in this instance. As with much of Scripture, the text contains levels beyond the literal reading, at the same time as also having a literal fulfillment.
When it comes to the seven churches, we in fact have no way of knowing for sure that the seven literal churches spoken of had spiritual conditions matching those that John describes in chapters 2 and 3. For example, was the Laodicean church of 100 A.D. as materialistic as it is portrayed? We can never know for sure, in which case the possibility is left open that the description given of it is as much symbolic as it is literal. This possibility becomes more of a likelihood when we look at the etymology of the church names. For example, why is it that the church named Philadelphia just happens to have a character that matches the meaning of the word Philadelphia? Or why does the church named Smyrna have tribulations which are implicit in the meaning of the word Smyrna? And why is the church named Laodicea in a state that mirrors the meaning of the word Laodicea? Why couldn't it have been the other way around? These questions tend toward a symbolic reading, without denying a literal reading.
This is a most ambitious project, but one in which we should all learn a thing or two. The Revelation is a tough book to decipher because of its thick use of symbols and its intertextuality with the rest of Scripture. May God bless our efforts as we seek His understanding!