During the six years of development, "Spencer" was the "in-between" stage of the original pitch of Dude, That's My Ghost! (aka Spencer's Spooks) and the final product that we have today. Spencer was the same cartoon as DTMG, but it had a severly different story than the happy-go-lucky and humorous show that we love--it was actually somewhat dark, in a sense.
In Spencer, Dirk (now known as Billy) was Spencer Wright's deceased rockstar/ghost guardian angel. In this version Madame X was also a ghost and haunted the Cobra Mansion as Dirk's spirit stalker. The main plot of this version was seemingly that Dirk, with a burning passion, wanted to finish his last album before passing on from earth. Hope this quick dose of DTMG history cleared this up for ya. Best wishes! (-: