You're increasing your attack surface area. Do you use both, do you let the server choose, do you let the client choose? What if the client requests the lower-security crypto? What if what the client asked you is different to what you think you were asked from the client (MITM)?
Yeah, setup one channel and then another inside that. Seems like hash functions could be used this way, too. For instance, are there any practical attacks in sight that'd work simultaneously on both MD5 and SHA1? 3DES does this with DES so it probably works in general?
This gets complicated fast, especially with hashes[1]. Like most of crypto, you shouldn't do it unless you have a team of experts who publicly vetted the algorithm and implementation.
