CHarred Vale is a time burner , there are 2-3 mithril nodes , and after u mine them u wait for respawn ..etc , incredibly boring ..... i would only recommend it if ur under lvl35 .
If you're over lvl40 go to Alterac mountains , where the Ogres are , good drops , good XP , and 4-5 mithril nodes at all times , plus TONS of iron around the mountains , and some truesilver/gold . Thats the place of choice .
If you're over lvl45-50 go to Tanaris and run through the edges like another member posted , you'll find at least 7-8 nodes from the bug place in south east to the southwest (Ungoro entrance), theres one small thorium vein also , and for some reason the Nodes in Tanaris drop Star Rubies more often .
I've tried all of the above , get away from Baflands like the PLAGUE , its a waste of time , the regular mobs drop **** and are annoying (stealthy tigers), no XP , and the dragon whelps and elite dragons hit VERY hard and give little loot for very few mithrils .