The historic Christian interpretation is that the 144k represents the sum total of all the Faithful. Every saint from all of history, as the people of God. The number is symbolic, 12x12 for the twelve tribes, multiplied by a thousand, which is typical of meaning "a great many", this group is the same as the "great multitude" mentioned in the same text. Such as when we read that God owns the cattle on a thousand hills, the meaning isn't that God only owns a thousand hills' worth of cattle, but that God owns all of it.
Likewise, this has been the traditional position of the Christian Church for most of its history, with the exception of some early Chilliasts, that the thousand years mentioned in the Apocalypse is, likewise, an indefinite period of time; and it refers not to an earthly reign of Christ, but to His present reign from heaven and that He exercises His kingdom and dominion now through His Church. Thus wherever the word is preached and the Sacraments administered, there Christ is, ruling and reigning as Lord and King.
You're right, the Apocalypse is a firmly symbolic, figurative text. By the very nature of what kind of literature it is, namely apocalyptic.
-CryptoLutheran