I purchased four tickets several weeks ago on the HA website. Checked again tonight and the fare has gone down about $175 per person !!! Called HA to see if they give any sort of credit voucher (as AA does) when a fare decreases. I was shocked to learn:
1) Once you book online, an HA res agent really can't make any changes to your reservations using any fares which are shown on the website. She wasn't even sure she could make a seat change (but did). So, apparently if you book online, you are stuck with that fare even if it goes down substantially.
2) She advised had I made the reservations by phone and the fare went down, they would give a credit voucher for the difference LESS $150 A TICKET SERVICE CHARGE !!!

So if you're contemplating a trip from the mainland, either be prepared to live with the fare you purchased or travel on another carrier which does issue vouchers for fare decreases. Other than this shocking information, I've always been happy with HA.

Thanks JIMCHI for the tip. I've always known HA to be a stickler on price differences... Does also sound like you got an incompetent agent. HA phone agents can and have made seat assignment changes in the past pretty easily (it's a shame you can't do this online until online check-in).

aloha