I went there for the first time a couple of months ago and had an awesome time. Here's what I recommend.
I noticed that you got a good deal from AMEX, but this is a great thread to check out just in case you're looking for hotel deals:
hotel deals. I stayed at Flamingo when I went there. The rooms were nice and it's located right in the center of the strip (opposite corner of Bellagio) so it's a great location. I'm planning on going back to Vegas later this year and will probably look at that thread again for deals at Venetian, Bellagio or the Wynn. The deal going on right now for Venetian for $98 per night is probably the best deal for a luxury type hotel. Unfortunately it ends in September and I won't be there until November or Dec.
I went with a crowd that doesn't party but it was still a lot of fun. If you like sightseeing tourist spots, you should check out the bus tours. We went to the Hoover Dam and it was pretty cool. If we had more time, we would have definitely checked out the Grand Canyon but I heard it's a 4 mile ride each way.
Most buffet places are good there. The Rio buffet was good (my friend liked it a lot). Flamingo buffet was ok too. The breakfast buffet at the Bellagio is probably the best. I really wanted to go back a second time. The wait was about an hour but it was definitely worth it. The line to get in was huge!
If you get tired of walking, you can take the bus (called the Deuce). It's $5 unlimited ride for 24hrs. We were in a rush to meet up with other friends on the opposite of the strip for dinner/shows so we ended up taking the bus a lot. But walking the strip is awesome though.
The gondola ride at the Venetian is very nice. I'd definitely recommend it for couples. If you need more ideas, pm me.