I know this is probably coming too late but I thought I would add to the topic anyway...
I've been in the industry for about 9 years now, started out as a Student member of the RAeS then became graduate member and now i've dropped membership.
I always wanted to be chartered when I started the career, so pursued the RAeS route. Looking back I found them vaguely useful, the company I started in gave out professional development folders that helped log all of my work experience in order to make the step to chartership easier. This folder was from the IMechE. I found the RAeS quite vague in how to get chartership through them, they just said apply after a couple of years of experience and we'll see. No guidelines, no thoughts, no baseline to see whether I was on track or anything. Yes, I understand that professional development is a large general arena, very unique to each individual, but it would have been nice to at least see something to point me in the right direction.
I agree with the sentiments above, it's great for networking. It didn't help my career one bit, hard work did that. The resources can be very useful, and some of the lectures can be very interesting.
I dropped my membership when I decided that I wanted to be a pilot. I'm still an engineer at the moment and don't miss the membership. I know that the only practical career progress that being chartered produced from the jobs I've had in the past is the ability to sign Airform 100A's (certificate to allow flight trials)and to sign off designs. Other than that I didn't notice anything else.
It has it's uses, whether they are for you is something you'll learn overtime. It won't hurt to get in and see. Rather than never knowing.
Bear in mind the advice to join before you graduate, it is much easier to get in as a student than after you graduate.