This is a waste of your time, and not worth all the hype in all the travel magazines. The store has limited options, and in all honesty you can find absolutely everything there for a lesser price, if you keep looking. The free trolley runs about every 20 minutes or more, so if you're done shopping there, it's a pretty boring wait for the trolley to arrive.
Fun Alternatives: Look on the side streets - they generally have cheaper stores, with the same things that you can find in all the touristy stores. Talk to someone you know who has been there before - they might have a good idea of where to find good deals. My mom found a fabulous pearl warehouse where you can find peral jewelry for more than half the price of the other stores! You just have to look!
You won´t be able to avoid Hilo Hattie´s - 'the store of Hawaii'. They are everywhere, selling their dreadful patterns and style to whoever cares to pay their high prices. In Honolulu, you can catch a glimpse at their sweatshop.