When I've had a United Airlines Red Carpet Club membership, absolutely the most valuable benefit to me was access to the lounge agents during irregular operations.

Currently I have the same Priority Pass membership that you do through Citi Platinum AMEX. I expect that access to lounge agents in the Premier Pass program will be statistically less likely to be useful than a regular airline club membership. When you pay for a regular airline club membership, after all, you'll likely do so on the airline that you fly the most and therefore the most likely to have lounge agents that can provide special help to you on that day's flight(s). By contrast, Premier Pass contracts with different lounges in different airports, and often it'll be with a company that isn't your airline. In non-US airports, in particular, it's common for Premier Pass to contract with a lounge that isn't run by any individual airline at all, but rather run by a company specializing in providing airport services, who contracts with not only Premier Pass but also various airlines who want a presence for their premium passengers at that airport but can't justify running their own facilities. Such a lounge's agents may be pleasant human beings trained to be helpful, but they won't have the computer access to help you in the same way.