I am Diamond, and I pay a corp rate of $130++. In Sept I had 2 stays at the Erawan; the 3-night stay was in a suite with RC privs (suite upgrade cert, not confirmed until check-in), and a second 1-night stay was in a regular room w/RC privs.

In between, I stayed at the IC, where I'm top tier and had a corp rate of $101++. I was upgraded to a suite, but no club privs.

For me, the ambience and terrific food in the Hyatt lounge trumps a no-lounge suite at the IC. YMMV. And it's not a burden to stay in either joint.