What's your Star Alliance status? I assume if you fly international much - or are paying for RCC membership - you get plenty of miles in. If you're a 2P or better on UA, and thus Star Alliance Gold, you can use all of the international clubs just by using your MP card.

I have a lot of international travel and I let my RCC membership expire two months ago. Between the Lufthansa Club at Dulles on domestic runs - where I can go in for free just for being Star Gold and traveling on UA - and international flights where I can use RCCs, I haven't missed being a paying member.