Just throwing my two cents in (because that's all anyone's opinion is really worth), I would book the lowest car category you can live with and then wait for an upgrade option at the counter.
When we were at Aulani two years ago over President's Day, I managed to move from an intermediate to a convertable for about $10/day. I would imagine with the massive decrease in tourism due to the pandemic, car rental agencies in HI are probably desperate for business and it's likely you'd be able to move up from your reservation to what you really want, for much less than it would cost you to book it now.
Or I could be totally wrong...