Have had the same issues recently - held for 20-30 minutes to make a new booking or change existing ones, which was rarely longer than a three minute wait using the old phone menu.
While travelling yesterday my flight was cancelled and I was rebooked with a downgrade to economy as aircraft had Y cabin only. I sorted this all out at the lounge desk, but 45 min later received an SMS to call 1300659115. This got me through to "Qantas Premium" answered in a very strong Aussie accent with less than a 30 second wait.
Despite calling what appears to be a special number, and entering my QFF# and PIN, the rep didn't seem to have any information to indicate what I was calling about - so what is the point of the special phone number? If it's just to connect me to a competent rep without much of a wait, and if the wait time for WPs doesn't improve, I might try call this number again next time I need to make a change...