Nick & Xander gel so well because both have powers they cannot explain. Xander has always been able to coerce others with mind control to get whatever he wants, while Nick is a chameleon-like shapeshifter who can blend himself into anything with the ability to algebraically plot large impossible schemes quietly from the shadows. What they share is a guiding sensitivity to events and people.
[[The real problem I find is in differentiating between memories, dreams, thoughts]]