Yeah - i doubt it will be a smash hit + all but surely it should do better than AvP:R, but i doubt it reaches the 80 million that AvP pulled in. I know people who are interested, but it's the same people that were interested in see the last 2 films. The Alien/Predator films have always proved to be global, so a domestic total around 45 million won't kill the film, but it won't bode well for a sequel.
I frequent Box Office Mojo + Box Office Prophets a lot, they're usually pretty good although have been way off in their estimations before. BOP often predicts the top 10 films of a given month, so i'll keep a look out for their take on July.
I agree that Predators has a lot going for it + certainly has us (the fans) behind it. Awareness is pretty low though. My dad knew of it but had no idea it was coming out so soon - hell, The Expendables has been advertised to death during the NBA finals + it comes out a full month later. Also, as mentioned the film will be facing a lot of competition it's opening weekend, as well as the following week (Inception - which i have no interest in, but surely others will...)
I certainly wouldn't be too disappointed with an opening of 20 million, although for it to really be considered a success i'm hoping for an opening closer to 30 million.