Note that Elevate will only exist until 12/31/17. At that point you will be converting Elevate points to Alaska Mileage Plan miles. Virgin Australia is as of yet not an Alaska partner (and it's unlikely to happen since Alaska has a longstanding relationship with Qantas).

Also... how are you getting from TPA to LAX? Virgin America doesn't fly that route. Most Virgin Australia partners who do (like Delta) won't be creditable to Virgin America or Alaska. So you may only be able to credit the LAX-MEL-LAX flights. (In that case I would strongly consider crediting your flights to Delta, not Alaska through a Virgin America conversion- despite all the naysaying about their program, unless you have ways to frequently credit to an Alaska account, Delta may be a better choice for someone based in Tampa given that Delta has many more service options out of TPA than Alaska does, and the Alaska partner that is most meaningful out of TPA, American, is arguably worse on award availability than Delta is).