No point in adding more seats if they can't sell out their games.
Exactly. Auburn fills capacity about twice a year now, with the other six home games having thousands of empty seats. Hell, their season and conference openers last year had something like 6,000 empty seats. Basically unless they have someone like Alabama, Georgia, or LSU on the schedule, they have thousands of empty seats.
What they really ought to do is expand-via-contraction. Scale the thing back to about 80,000 or so and just make it incredibly nice. The thing about Auburn is that they don't have any issue selling suites, they just cannot sell seats. It's a common-sense solution. Remove seats, add suites.
Of course, though, there's no chance it'll ever happen. With Alabama expanding to 100,000+ with tens of thousands on the waiting list, there is no way they will ever swallow their pride and reduce to where they should be. They'll consistently have a sea of empty seats before they'd ever even consider doing that.
And, actually, truth be told, that is the only reason they ever expanded that much in the first place. Auburn originally expanded to 87,000+ in the late 1980's, for Christ's sake, and never had any need to do so then. At no point in the history of Auburn football have they had the fan base needed to consistently fill an 87,000+ seat stadium eight times a year. They've struggled to consistently fill that place for over twenty years now, even in the glory years of 1993 and 2004. Even with the TV ban in '93 they sold out only one game (Iron Bowl), and they even had empty seats in the stretch run of the '04 campaign where they were firmly in the mix for a national championship.
Again, though, they were always trapped in their little brother need to one-up Alabama. It never had anything to do with legitimately trying to optimize capacity by matching long-term supply and demand. Remember, at the time Legion Field (the real "home" of 'Bama football then) held 83,000, and Bryant-Denny only held about 70,000. So by god we're going to build ours out to 87,000! Who difference does it make if we can ever fill the place up, we've one-upped Alabama, right?