Be careful of the naming of the course as there seems to be a whole range of names applied here. The ERC is generally regarded as course after the BRC. Where I took it they called it the Experienced Rider Course (which is the same as the IRC).
MSF has just developed a class after this with more advanced techniques. I think my local place is calling it the Advanced RC but I have seen someone calling it the Advanced Expert RC, which is a hell of a mouthful (not to mention making it sound like a class for the top 5% of riders).
For what its worth, I thought the intermediate class (whatever you want to call it) was only marginally worthwhile. It is essentially the same as the BRC with the really basic stuff taken out (walking the bike, friction zone, cheesy class room videos). Most of the exercises are the same with the exact same instructions. It is good to get feedback on how you are doing but it is really just reaffirming what you learned in the BRC.
If you have been doing PLP by yourself, can do the box, weaves, emergency stops with no problem then I would go skip the intermediate class and go straight to the advanced one.