While I fully concur that the Scripture teaches that Noah was a preacher of righteousness who preached to the ungodly people of his day, there is something else being taught in 1 Peter 3:19ff. First, the passage is (of course) connected to verse 18, where we are told that Jesus was put to death in the flesh, but made alive in the spirit -- a reference to His death and resurrection. So the introductory words in v. 19 ("in which also" in the NASB) refer to the post-resurrection Christ. The verb "went" is used in other places in the NT to refer to Jesus' ascension (e.g., Acts 1:11; also note the context of 1 Peter 3:22); while this common verb can refer to other "goings," it is very important to note that it nowhere in the NT does this "going" refer to a trip by Jesus to the netherworld. Next, the verb for "preached" is not the ordinary one used by Peter for the preaching of the good news; instead, this verb has the more common meaning of "to announce." The "spirits" referred to this verse (in the plural form), which only a couple of exceptions, refer to supernatural powers in the NT (either angels or especially demons). "Now in prison" is never used in the NT to refer to a place where human beings are kept after death (but it is used, for instance, in Rev 20:7 to refer to a holding place for Satan). If we put all of these pieces together, and let Scripture interpret Scripture (see, for instance, Colossians 2:15 and 2 Peter 2:24), the picture that is being given to us is one of Christ's victory over the powers of darkness in His death, burial, resurrection, and ascension. This fits well with a later verse in the same passage (1 Peter 3:22), it is consistent with one of the major themes of the NT, and follows one of the underlying themes of 1 Peter -- to encourage Christians who are undergoing persecution for the gospel to endure; because Christ was put to death but emerged victorious, they will be victorious in Christ, and need to stand firm in the faith, which they are able to do because of Christ.