I suppose the first question would be what do you intend to run on it? I would think you would want a single server and without a substantial reason to avoid this I think it's the way to go. OTOH, if you plan to run mostly CGI scripts and have some really large funky limited use handlers then by all means run 2 copies.
If you are not preloading tons of modules I don't think the overhead increase would be much at all.