Omen of clarity is a good choice right at the start imo. If you get your Clarity up you can easily heal yourself and keep on grinding.
Leveling up a feral druid is easy as sin, but I'm afraid I'm going to have to disagree with this sentiment. A player that focuses on as much strength as possible from gear (hard to get while leveling in vanilla), with agility+stamina as the other concerns, there's pretty much no problem with mana while grinding / questing. It's a sad fact that spirit ends up on a metric crap-ton of quested and crafted gear, whether we want it or not. Carefully pacing heals after every 4th kill or so recovers all the mana you'd care to want while in animal form.
If you want Omen of Clarity for reasons other than mana for healing while grinding / questing, go for it. I simply had no use for it for the leveling stage of the game.
I personally shoot to have the following for level 41 as a goal.
http://www.wowprovider.com/?talent=11215875_11_8q5d521303222151p
After that, grab what you want. Improved Shred IS useful if the private server has mobs correctly not spin to face you when they're stunned from a Pounce. With improved shred, you can Pounce, Shred, Faerie Fire, and Shred if you have Brutal Impact 2/2. This is kind of a really BIG deal when you want to grind on mobs and take very little return damage, as they're already half dead from your initial energy burn.
It's also immensely satisfying for open world PvP use. Unless your target is a Warlock, the Pounce - Shred x2 - Faerie Fire combo starts off a fight in a really sour position for your target.
Edit - I mention warlocks specifically as a bad target to fight as that class has too many big fat "I Win" buttons against a feral spec druid. I simply leave them alone unless I can get them at a good time with their being low in health or mana, or preferably, both.