One problem with that approach is that you wind up flying on two itineraries. And if there is a problem with flights, you can get left hanging. So let's say that you are flying to a west coast portal on a Friday, with an early afternoon arrival. Maybe you have two to three hours layover before you catch a connecting flight to, on your other ticket.
But then there's a problem on your outbound flight. Mechanical problems, bad weather, whatever, and suddenly you can't make the connecting that flight. If you're booked on two itineraries you're screwed. Your first carrier guarantees you transportation to the connecting location, and that's all. They will rebook you to that location in accordance with their policies - and if that means you can't make the connecting flight means nothing to them. Meanwhile, the connecting airline will simply treat you as a No-show, and may cancel your ticket, including the return flight.
If you book transportation to Hawaii as one itinerary, if there is a problem on the first flight, the airline is still obligated to get you to your final destination. The only time I break up an itinerary is if I'm going to have at least a day on the ground in the stopover location.