Yep, what Mish said. You actually do not apply for a 309 from a 300... you apply for an 820 (Onshore partner visa). You obviously can't apply for that right now, offshore.
The disadvantages (as Mish said) are that they'd then be looking for more/better evidence, and that they are actually under no obligation to even look at anything more you send them... they are allowed to make a decision based on just the information they have at any time. They'd probably take any additional evidence you sent in into account... but you're taking that chance, and you're just complicating things for yourself. Probably far better to just wait it out...
Original Nationality: US
Visa #1: PMV (300) through Washington, D.C
Applied: April 2013.
Visa Granted: January 2014.
Visa #2: Subclass 820 (From PMV).
Applied: End of April 2014.
Visa Granted: Early July 2014.
Visa #3: 801 (PR)
Eligibility Date: End of April 2016 (Applied a month prior).
PR Granted: Early April 2017.