As a former IML status holder, I stopped accruing after I saw miles expire. Despite flying in business on EVA 2-3 times a year, I was only able to redeem one time over the period of 3 years I was doing that. I live in Canada so my circumstances are different., but boy oh boy, I have never forgiven the carrier over the loss of my miles. IMO the IML program stinks. There is not much there to encourage loyalty compared to other airline programs. My miles will never expire with AC Aeroplan (for now) and my benefits as a Gold with the airline, while not great, beat what EVA offered.
Status with EVA will give a customer some better service during IROPs and perhaps a more hospitable treatment than with other carriers. And that's the catch with EVA, because I can honestly say, I have always been treated decently even without status. I only fly business when selecting EVA, and despite some complaints, consider it a wonderful carrier. My point being that status gives me nothing that I would already get at EVA. As for the redemptions and availabilities, yes EVA favours its own FFs. Unfortunately, this is all part of the sham of the airline alliances.
To sum up: Great airline, crappy loyalty program.