Hawaii does have lots of fiber. Monetary costs for circuits between Guam and Hawaii are not ignorable. Also, back-haul all the way to Hawaii for an intra-Asia interconnect causes a significant increase in latency when compared with a Guam-based interconnect. (No, I've never been to Guam and I don't own any land or fiber there :-)
My Big Map o' Fiber(*) shows the HAW-5 cable going from L.A.-ish (probably San Diego?) to Hawaii, and then continuing on to Guam and then Japan as TPC-5. The Pacrimeast cable leaves Hawaii bound for Wellington, NZ, and the Pacrimwest cable leaves Guam bound for Sydney/Canberra. Tasman-2 then connects Sydney/Canberra with Wellington. Both Pacrim cables and Tasman-2 are a LOT skinnier on the map than TPC-5 or HAW-5. Why does it have to be an either-or? Topologically, it looks like both Hawaii and Guam would both make sensible exchange points. For the west side of the Pacific Rim, though, Guam is looking pretty good from a U.S territory perspective.
From an infrastructure perspective, though, Japan looks hard to beat. The pipes to Singapore/Jakarta/Australia, Guam/Hawaii/L.A.-ish, and somewhere in Oregon (?) all meet there. Ignoring regulations, tariff issues, etc., of course.
Stephen (*) Telecommunications Map of the World, produced by The Petroleum Economist, Ltd., London, and Telegeography, Inc., Washington D.C., in associated with Ing Barings. Truly a stunning map, and it comes with a thousand pages of paragraphs with circles and arrows explaining what it is.