Congrats OP! I got the Plat back in June (the MB co-brand version), and was charged the $475 (in my case,for you it's $450) on my second statement. FYI my AMEX score was 677 at the time, but unlike you I was already an account holder, so it probably made it easier for my approval.

It's been < 4 months, and here's what I've gotten back so far -

* Same as you, the Delta $200 back with 2 upgrades to EC, and a bunch of alcohol on the trip + the fruit and cheese plate and sandwiches  

* Same trip, got in to the Delta lounge with my wife, which is normally $39 each person = $78

* Did an FHR night in Vegas for $120, and got $60 credit for breakfast and $100 credit for spa services = $160

* I got 50k points bonus (promo at the time for MB Plat) = minimum $500

* Got a $100 service gift cert for MB (my wife has one), used it on our next service that was otherwise on sale for $189 = $100

* Got a $1k MBUSA gift certificate towards next MB lease / buy, no matter what other promos are on. Same as cash. Won't be using anytime soon 

* Got 12k more points from purchases = $120 minimum

I'm sure some of you won't agree with some of these valuations, as I actually wouldn't have gotten them if they weren't free so it was more of a "perk". Regardless, on the high-end, if I counted everything, it's $2158

The more realistic figure, removing everything in red above (I wouldn't have bought otherwise, or doesn't apply), what I've gotten back is $980.

Now, a big chunk of that is the sign-up bonus. Not sure I can replicate it next year, so might cancel unless I travel a lot more for some reason next year.