I know this is almost a month after the question; however, I just couldn't help but chime in as it seems we have varied opinions.
I agree with Sierra that if you come to Vegas to basically gamble, then being Diamond is certainly no big deal.
However, if you come to Vegas for the "whole experience" of food, liesure, pools, bars, and such, then I would like to say that being a Diamond player is the best way to enjoy these as long as you plan go visit four or more times a year:
Diamond Lounges: free drinks, good TVs, and though the snacks are an embarrassment when compared to Atlantic City, they are there and they are...free.
Diamond Check-in are SO much faster than regular. And yes, don't underestimate the Diamond lines at the buffets and cafes. They easily save you as much as an hour at PH and Paris and the Rio.
When valet is full, Diamond is allowed.
Here's the clue one which place to get your Diamond IF you insist on getting it in Vegas:
When your comps start coming in (about two to three months), there will be two different types. There will be a coporate magazine, which has assorted comps based on your daily average play with free nights in Vegas as well as other CET properties in the country. Then there will be the offers that come from the place you got the Diamand, which are seperate from the corporate ones. These include free nights, slot/ VP/Poker tournaments, and other things like buffet passes, $ off restaurants and such.
All of the Vegas properties have pretty much the same VP schedules (except the Paris, which are the worst), and I'll assume the same for slots. If you're a slot player, pick your favorite place. If you're a VP player, the same (excpet the Paris). Poker and Table players suffer trying to get Diamond unless you're a black chip and up player.
If all you want is the Diamond in the Day (4000 points in a 24 hr period) and you're a VP player and don't care how you get it, make a reservation and go to Harrahs, Rincon. The have a wall of full play VP from $.25 to $5.00. Get your Diamond and use it for a year.
That's my two cents.