Do you need an outboard preamp? No not really.
As somebody already mentioned, owning your own DI will come in handing if you're out doing the club scene. This can work as a more affordable back up to your main amp instead of lugging around a second amp. Also, a DI/outboard preamp can save the day if things go horribly wrong at a gig.
Carvin Club #167
Switch-Hitter #25 (musical switch-hitter you pervs! Musical!)