I think that the main thing is to see how much you'll miss the 18-24 range. Check your files and see how often you use that range. Whether or not you use it a lot, you'll know something. Also take note of how often the 18 and 70 are used - if they are a lot more than the lengths near them, you probably were in need of something wider or longer. The 24-120 obviously offers one of those, but not the other.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!