Over the course of the next ten years, a number of attendance related factors for Disneyland will likely occur.
1) Sister park, DCA, is receiving a major injection in the form of capital for an overhaul of certain areas, improvements and expansion.
2) A third theme park and waterpark may well be built and open by that time.
3) By then, there will be quite a few new rides and other attractions (including high capacity ones) at Disneyland itself. We expect the rumors shall ring true about a new ride for the PM tracks, a new Star Tours, and one or more attractions for the former Motorboat Cruise area. There have also been significant rumblings that predict new rides for Frontierland...including an expansion onto new property.
4) There are bound to be advances in crowd control mechanisms, such as FastPass and other avenues.
5) Other factors.
Let's consider the expansion of the overall resort in terms of rides, attractions, a possible new gate (and waterpark)...and, subsequently, an increased crowd handling capacity in relationship to today's attendance figures.
The question to ponder is... would the new rides and shows be so popular that they would drive attendance up high enough to offset the increased ride capacity? If so, would FastPass and other forms of crowd control make up for any dramatic increase in attendance?