To say it's a waste of money isn't competely true. Would I pay it - no.

But let's say you are a frequent commuter on sub-500 miles flights with easy F upgrades. That's 15 round-trips a year to make Silver status. Let's say you plan on it once a month next year and would loose status without paying the $899. That's less than $50 a trip for an F upgrade, preferred boarding, check-in and a lower club fee. In some airports those things mean nothing. In some they mean a lot. People value F at different values but even on a 45 minute hop it's worth something - esp. with runway delays that can easily leave on the plane for much longer than the flight time in airports like PHL.