The one time I've been lucky enough to be evacuated from an attraction was for The Many Adventures of Winnie the Pooh at Disneyland. The lights on didn't change anything much, but getting to walk to the exit made it easier to find a hidden Mickey, as well as spend some time looking at the Max, Buff, and Melvin heads "hidden" in one of the rooms.
I have, however, been lucky enough to see most of the attractions at Disneyland with the lights on and walk through them. Disneyland held a special employee night and allowed us to get a behind-the-scenes look at a lot of the best ones. Haunted Mansion was great, especially the "ghost will follow you home" part. How they did it surprised me. I figured the ghosts were just projections.
We were also allowed to ride Space Mountain with the lights on (very plain, but cool anyway), walk through Roger Rabbit's Cartoon Spin, walk through a small part of Indiana Jones (I was also surprised at how they do the beginning door effect), and watch the Star Tours cabs in motion from the floor. They reminded me of bu-cking (I had to put the dash in their or the dirty language police attack for some reason) broncos and seemed almost alive.
I have some pictures of behind the scenes stuff on Star Tours, the Submarine Voyage, Mission to Mars, and maybe a Space Mountain shot or two, but they were taken with a disposable camera, so aren't exactly worth posting.
Personally, I don't feel it ruins the attraction to see it with the lights on. For me, it enhances it, because I can see the work and detail put into it.