As a UA MileagePlus™ Premier Silver member for the better part of a decade, I concur with the foregoing.

I do like Economy Plus (E+) at check-in; it helps to pick less-popular flights, and to "babysit" the seat map during those last 24 hours. Group 2 boarding is nice, too.

To me, the other principal benefit of being a Premier Silver is the 500-mile minimum per segment for lifetime mileage accrual purposes.