I have to agree with Dave about the cables. Dropping thousands of dollars on a PAIR of cables seems terribly excessive. Since cables are so light and portable, it's easy to borrow from a friend and take them for a test drive.
Other overrated components? When I was looking to audition some Rotel gear 3-4 months ago, I listened to the newest Quad ESLs with some pricey CJ gear. Did it sound nice? Sure. Was I blown away by the 20+k system? No.
I'll add some fuel to the fire and state that just about any component (with the exclusion of speakers) that is north of 10 grand is very likely to be overrated. Many magazines and reviewers don't audition equipment unless it's in the 5 figure range, and this is sad. That price point is way out of reach for most people, and very often the equipment doesn't live up to the hype anyway.
In my opinion once you start dropping over 3-4k for an amp, cd player, DAC, etc what you get in improvement for each increment of hundred, or thousand, dollars seems less and less.
Why would you exclude speakers from the over-rated group? Should I spend 5K on a CD player, pre and amp and hook them up to 15K speakers? That should definitely let me hear all the flaws in the upstream gear!