There are probably a combination of things that draw people. For one thing, I still like Omni rides with sets or screens. I'm not implying that everyone would dismiss them, however, if you look at the factors that influence discussions here, you will quickly see that if what was built in the 80's would no longer be either sophisticated enough or technologically advanced enough to meet the muster of today's theme park connoisseur. Also, with SSE, there is the classic factor, again nostalgia, I really doubt that if that same thing were built today without the benefit of past experience, it would not go over very well.
Another element is the uniqueness of the SSE building itself. People would probably go to see a landfill if you got to ride in a huge globe, so actually, I feel that the substance of what's inside does not always create the demand. Also depends on when you go and what time you get there. I can assure you that there still are plenty of times when SSE is anything but "packed". It's still a must see for many people like myself, but, you are not likely to see people sprinting from the gate to it like has happened recently with Soarin' and TT.