Custom water cooling is usually overkill in most cases, but with extreme overclocking (like everyone who has a water cooling rig probably does) the motherboard actually kind of needs to be better cooled.
$600!?! Where exactly are you buying it? Newegg has it for $399. This is probably the highest end Z77 board on the market. For $399 I don't think that's asking too much... I own this board and love it. If you want a full chipset waterblock, outside of the ROG ASUS mobo's, there aren't many z77 mobos that are compatible. Top of the line Mobo, with the option to buy a Full chipset waterblock. Sign me up.