You can do anything you want, you don't have to be cookie cutter. Mix things up you'll never know what you might like. --- Worst moderators in this history of message boards, trolling you right here on gamefaqs.
Depends who you're facing, but in most cases if you're confident enough in your ability to use her that you will suffer minimal harass then by all means, mix it up. --- Dojo, casino, it's all in the mind. [LoL: Syndra, Rumble, Volibear, Ezreal, Orianna, Draven, Fizz, Talon, Janna, Nasus]
Syndra's harass might be safe enough to not have any defense but her ult range sure isn't. Mana regen is fine though, buy defense if you need it.
And scaling health seals are better for general defense at mid anyway.
Gold runes are better than any scaling stats, honestly, besides maybe mana regen. Your extra gold gain will progressively afford you better itemization at a similar rate as scaling health boosts HP, except if you decide you don't need health in the middle of the game you can just use your gold to buy a different stat. --- "Pokey and the man."
Safe enough? Not really. You still can try it if you feel the need to be more aggresive. --- Amid the turmoil and tumult of battle, there may be seeming disorder and yet no real disorder at all Sun Tzu