Victor, I think you did quite well in capturing the concert, especially since you were working handicapped with a lens which has an f/5.6 as its maximum aperture when zoomed to its maximum focal length...
Even shooting with a lens that is capable of f/4 at its maximum focal length, it would have allowed you to cut your ISO in half and thus reducing the noise. An f/2.8 aperture would have been even better. However, we shoot with whatever equipment we have available and, unless the venue is very important or unless you are making money from the event, renting gear is not always the best idea. Also, using a rental camera/lens that you are not used to when shooting an event is a chancy situation...
IMO, there are two ways to cover a concert. First is images of the performers without showing the crowd. Second is showing the performers in relation to the crowd which you have done in image #1, That is a refreshing way to cover a concert because it gives me the feeling of "being there"...
I will be covering the concert that our Maltese Rescue California is sponsoring later this month...
I plan to do most of my coverage along the lines of your first image. Showing the crowd integrated with the performers.
I will use my pair of Canon 7D cameras and 17-55mm f/2.8 IS and 70-200mm f/4L IS lenses to cover the concert. Luckily, there will be some daylight left during the performance which will help me in using a lower ISO.
Since I am the secretary of our rescue group, I will be the person charged with interfacing with the security detail we are hiring for the concert. I am pretty sure that I will have carte blanche for non-flash photography. I definitely want a shot along the lines of your #1 image. Thanks for posting it. It has started my creative juices flowing. If possible, I'd also like a shot from behind the performers showing the audience.