I think what is needed is for Arbitrators to reevaluate their own participation each year. An Arbitrator who finds the workload more than they bargained for should probably step down when the next election cycle rolls around to free up a spot for someone fresh. Institutional memory is a good thing, but replacing 8 or 9 Arbitrators out of 15 should not be a hugely more disruptive situation than replacing 5.
That's what I was thinking when I was considering standing in the last elections (I decided not to, which was the right decision, I think - maybe this time... we'll see) - I didn't really expect to last more than a year, and didn't think it would be a problem to serve for a year and step down at the next election. Less than a year, and I would have felt like I was letting down the people who voted for me (if there had been any, which I doubt - I wasn't ready, and I doubt I could have fooled people into thinking I was), but a year is long enough, I think.