Let me preface my comments by stating that I fall into the unique category of a 50/50 enthusiast. While I welcome and advocate the addition of major coasters, I also appreciate the park's continued attention to detail, and would also love to see those efforts put forth with improvements to some SDC staples (e.g., TNT, FITH, FM & AP).
It's already been touched on numerous times in various threads, but the unfortunate truth is SDC simply cannot remain profitable without engaging itself in the ongoing large, thrill-ride race. They are competing for tourism dollars against other major amusement parks that already have an edge based on demographics, brand awareness and geography (proximity to major metro areas).
I firmly believe SDC will always have the charm others in the industry cannot come close to matching, but if you want to see the park carry on, it's going to require the continued addition of new major attractions.
I think you also have to consider that while SDC owns a considerably larger parcel of land than the park's current footprint consumes, there isn't a terribly obvious and convenient place for major park expansion. SDC's major coasters already skirt it's western perimeter, so I think any fear of pulling into SDC's main lot 20 years from now and seeing nothing but towering hyper coasters framing the horizon is unwarranted and unrealistic in my view.
In short, a whole lot would need to happen, before that ever happens at SDC.