I got the RHCE for RHEL 6 a few years ago and remember it being full of useless guff, such as configuring SAMBA users as well as users for other services, as well as iSCSI, etc. that you mention, none of which I've ever used (so, of course, have forgotten - it's hard to commit such rubbish to memory!).

And, while I've studied for the RHEL 7 RHCE haven't taken the exam yet, because it's expensive and full of much the same useless stuff.

It's probably good to learn a lot of the other, more useful stuff, just for your own knowledge, but I really don't think it's worth the effort, time or money to do all that's necessary for the exam (unless someone else is paying for it).

Probably looks good on the CV, but that's about it, IMO.