From your questions, it sounds like you haven't read many of the issues of EA. (numbering is to keep my thoughts straight and has no other meaning)
1) The EAs have included NEW material in almost every issue. Most of that new material has been in the form of new options, not optional core elements. Express Additions is to RMX/C what Rolemaster Quarterly and HARPer's Bazaar has been to the other systems, EA just had an additional purpose in its first couple of issues.
2) I have introduced a total of 3 skill over 7 issues. 1 of those skills was a general skill which could replace a number of specific skills that already existed (reverse bloat?
), and the 2 skills in this issue, IMO, can cover almost any sort of social situation, which is something that I felt the current skill list is sorely missing.
3) In all three cases, the costs for these 3 skills have been given for all professions.
4) In the make-over of the Ranger, the skill costs for ALL skills were given, as it was done to be usable for both RMX and RMC.
5) At this point in time, I don't see (or foresee) the need to add any more skills, at least not in the EAs (possible exception -- if I add some capabilities redone, like psifire or the Chi Abilities from Oriental Companion redone -- that might require skills for those specific additions). We now have skills that can cover most every normal situation.
I hope that covers your concerns.