As a fellow SPG Plat / Marriott Plat who recently got married, I can feel your pain... There really isn't a great option. I'll give you some other options / advice, though, and I'm sure you'll end up having a wonderful honeymoon!
1) Overwater bungalows aren't as cool as they seem. Yes. They're awesome. But once you're in one, the "wow" factor goes away, and it's just a hotel room.
2) If you're set on an Overwater Bungalow and you're committed to SPG, The Le Meridien Bora Bora seems to offer the lowest rates, but low rates are like $500 / night if you're lucky, at least from what I've seen.
3) How far away is your honeymoon? I'm guessing that as you're a Plat100, you don't like the idea of pushing stays to other brands, but here's an option. Get the following three credit cards: The Chase Sapphire Preferred Card + The Chase Ink Bold Plus Card + The Hyatt Chase Card... The Hyatt Chase card comes w/ 2 free resort nights at ANY property worldwide. Both of the other two chase cards come with 40,000 point bonuses. You can transfer those points to Hyatt. BOOM! Now you have two free nights + 80,000 Hyatt points to blow on the Park Hyatt Maldives:
http://maldives.hadahaa.park.hyatt.c...otel/home.html ~ Look at that - I just got you a honeymoon in the Maldives for basically no money - who's the man?
~ that leaves all those SPG points for you to get value out of them w/ some first class travel via airline transfer.
4) Want to use those SPG points for a hotel that isn't Starwood? Hilton devalued their award chart pretty heavily, but even so, the Conrad Maldives (I stayed there on MY honeymoon!) is a world class resort w/ seaplanes, an underwater restaurant, overwater bungalows and prices so high you'll crap your pants. Hilton also has the Hilton Moorea, which looks quite nice as well, but I haven't stayed there. You can transfer your SPG points to Virgin Atlantic. You'll get the 5000 point bonus for every 20,000 you transfer. I.E. 20,000 SPG points turn into 25,000 Virgin Atlantic points. You can then transfer points at a 1:2 ratio from Virgin Atlantic into Hilton. I.E. 20,000 SPG points -> 50,000 Hilton HHonors points. That's actually not a terrible deal if you really have close to 300,000 SPG points. Check the chart for details, but even if the Conrad is 100,000 per night, that still comes out to only 40,000 SPG points per night. I believe the Hilton Moorea would be less too...
5) I'm sure you have a fiancé who is demanding to be in an OWB (I know NOTHING about that...
), but if you can convince her otherwise, try something like the St. Mauritius. It's a top notch resort, and it's brand new. Also, my wife and I have once stayed at the St. Regis Punta Mita, and while you may not consider Mexico as exotic as an overwater bungalow, the St. Regis Punta Mita is amazing. Would seriously make a great honeymoon destination...
6) I think everyone would probably agree that if you're looking for the best combo of luxury + value, go to Thailand. It's amazing there. The food is freaking delicious. The resorts are awesome. The people are friendly. Plenty of airline options for you transfer your SPG points to for first class travel, etc.
ENJOY!!!!!!!