Between HNL and SFO, you would actually be looking for G inventory, not Z. If you were looking for Z inventory SFO-HNL on ExpertFlyer, that might explain why you found none.

Generally speaking, upgrade inventory to/from Hawaii is pretty good, and it's not too bad to many international destinations. The only problem is the M fare requirement internationally, as the M fares have been spiraling upward the last few years, which could be mitigated somewhat if there was ever an M fare sale.