One problem with finding an alternative is that most of the forums I’ve come across that have a more intelligent vibe are either political/religious/philosophical debate sites that are just giant versions of GD (Internet Infidels is a good example), or else they specialize in a very specialized subject matter that won’t be of interest to all Dopers (literature, physics, astronony, etc.)
I’d hang out at Fathom more, but the color scheme … c’mon, Opal! Unaboard is a well-run alternative with an intelligent SDMB-ish atmosphere, but traffic is moderate.