I think you'd be shifting the scope of their job towards moderation.
Unfortunately, when you are given the ability to moderate, you hold higher power than the rest. Your judgments directly impact on how others forum. This means that the community will hold perceptions of you.
Right now, Community Helpers (CH) are free from judgement by the forum community because they help out completely of their own volition and sacrifice a little bit of their time. The only merit they get is their title as CH, which represents that Jagex recognises their efforts.
If you start giving them powers, it might change the dynamic between them and the rest of the community.