^Exactly my situation, rarely ever use it. The trackpad is just so good, especially with BTT. I've thought of getting the external trackpad though, but I didn't think it was worth it for a MBP person.
Unless you plan on having the MBP hooked up to a monitor, and making a dedicated desktop space for it, then I don't think so.
If you do, MagicWand seems like a cool little thing to get to connect both the trackpad and keyboard together.