Well....
As a 27-year Oahu resident that moved here as a 21-year old motorcyclist I have to say there is good and bad.
The good - you can ride year-round, there ARE some nice places to ride & explore, and riding day-to-day is entirely doable.
The bad - You DO eventually run out of new roads on one island - ( shipping bikes interisland is fun but not that easy, the Ferry was great while it lasted) and the heat makes wearing gear a BIT of a humbug. Because of climate and peer-acceptance and LOT of young riders don't wear gear, and we all know where THAT can lead.
I like to ride - I prefer it to driving, even though I own a car and need it for work some days and for boat stuff, I'd rather be on 2 wheels anyday -it just makes me feel better. So, if the riding is nothing more than a driving-alternative that's fine with me. As far as WHAT you ride - I always recommend riding what you like - some don't feel the stoke at all even considering my lowly Wee-Strom commuter, I don't 'get' most cruisers - to each his own, ya know ?
As far as the drivers - there ARE a lot of distracted drivers out there, but I honestly can't say the visitors are any worse than anyone else on the roads, at least rental cars are easy to spot. That means you, late-model Mustang convertible. The Tuner-car race boys, blacked-out gangsta trucks, NPR-listening Prius moms, rust-bucket swerving mokes and idiot delivery trucks are all not to be trusted, as we know.
As for the economic aspect - yeah, it's hard to save money if you ride a sportbike, but you can ride pretty inexpensively if you really want to - I did as a college student back in '86 with a wrecked '82 Suzuki GS650E I bought from a roomate for a case of beer. If he is on base a scooter might be fine there (ride a bike) but won't have the legs to be truely useful.
You can certainly ride 'recreationally' here if you don't mind running the same routes frequently, and that is unacceptable to a lot of you - I get that, heck for fun on most weekends you'll find me offshore under sail, not squidding it up Tantalus, but that doesn't mean you can't have fun riding here - it's always better to ride when you can, in my view.
As far as 'getting out on new roads' goes, I actually keep a FJR1300 on the mainland for my yearly road-trip fix - I too need several days worth of new roads a year to keep sane. While the bike has been based in the bay area twice, it's near Philly now.
Feel free to have him look me up, btw - always glad to know another rider.
Oh, the REALLY good part ? Excellent vented gear has never been more affordable - you kids these days, you don't know how good you have it....