Scott Bullock set an unfortunate example with his untimely, unnecessary, dramatic demise of Big Debt, Small Law. If your blog is worth reading and has been around long enough, people have it cached somewhere. You'll never get rid of it. Meanwhile, you'll deny a dose of reality to newbies sorely in need of one.
Every time a blogger publicly calls it quits, the Valvoline Dean and his counterparts exchange metaphorical high fives. Unless you need to take your blog down for financial reasons — all babies must eat — leave it up and just walk away.