Don't take this the wrong way, but if it's a special occasion as you mention (wife's 40th), why wouldn't you just pay the upgrade offer now to confirm it and be done? You didn't mention if it's a weekend stay or weeknight stay. The concentration of Golds/Diamonds is slightly less on the weekends, but a lot of tourists will pay the going rate for confirmed suites as well so the upgrade inventory is still limited and even moreso for you as a Gold.
The Astor suites are nice, but on the small side. They are 2 rooms, separated by a pair of french doors, but both the living room and bedroom are rather small.
If they are offering an upgrade, you want to get at least a mini-suite or 1 Bedroom suite on floor 25 or 27 (26 is the Astoria level that has those suites too, but probably a higher upgrade charge).