I don't see how castling can be over-rated when it (usually) places the King in a safer position, helps develop the castled Rook and helps to get the rooks connected. However I would think twice about castling if the Queens have already been exchanged.
If once a man delays castling and his king remains in the center, files will open up against him, bishops sweep the board, rooks will dominate the seventh rank, and pawns turn into queens. Irving Chernev
As long as my opponent has not yet castled, on each move I seek a pretext for an offensive. Even when I realize that the king is not in danger. Mikhail Tal
Castle if you will or if you must, but not because you can H N Pillsbury
Castling is overrated. It's often a necessary move, but too many people think that castling ASAP is a must, and often they are killing themselves.
A lot depends on the opening being played.
Take the following openings ...
King's Indian - 1.d4 Nf6 2.c4 g6 3.Nc3 Bg7 4.e4 d6 5.Nf3 O-O
Nimzo-Indian - 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.e3 O-O
KIA vs French - 1.e4 e6 2.d3 d5 3.Nd2 Nf6 4.Ngf3 c5 5.g3 Nc3 6.Bg2 Be7 7.O-O O-O intending Nd7 (if White plays e5), b5, a5, Ba6, b4, etc.
In each of those cases, Castling is part of the opening itself. However, there are other openings where castling too early is a mistake.
Modern Defense - 1.e4 g6 2.d4 Bg7 3.Nc3 d6 4.Be3 a6 5.Nf3 b5 intending ...Nbd7, ...Bb7, and ...c5. Black doesn't want to develop the King's Knight just so he can Castle too quickly as it prevents Bh6. It also leaves White guessing whether you'll castle Kingside, Queenside, or often not at all! I've had many games where I didn't castle, and was fine, either drawing, or sometimes outright winning!
KIA vs Sicilian - After 1.e4 c5 2.Nf3 e6 3.d3 Nge7 4.Nbd2 g6 5.g3 Bg7 6.Bg2 Nc6 7.O-O d5 8.Re1, 8...O-O is a known error due to commitment too soon. White has a ready-made attack, and just has to time e5 right such that Black can't play ...g5 in response.
So long story short, it depends!