I've been to WDW, DL, and DLRP alone many times. Work brings me to many locations around the world, and I have always enjoyed travel.
While I enjoy my trips with friends/family, I also enjoy trips alone. They have a different flavour to them.
Of course, I have been to the parks so often that even with my usual Disney friend we don't rush around - we just go where we want and wander around at leisure.