I have a 98 190 with the LT-1 (350 HP) in my 30th Anniversary w/ 1:1 transmission. I have 670 hours of trouble-free engine performance to this point. I love to go footin and slalom, my wife and kids wakeboard and kneeboard. The boat does everything we want it to do. I generally go footin at around 40 mph and it gets me there fast enough.
Drawbacks to the LT-1? I don't know of any other than you have to watch the temp gauge since the engine has aluminum heads. The cooling issues you mention were solved wth reverse cooling. I can't remember the specifics of that off the top of my head, but if you do a search on here you will find several threads on the topic.
As for the premium fuel...it is 0.20 more per gallon x 24 gallons in my tank which makes a fill up $4.80 more.
I hope this helps.
1998 ProStar 190 30th Anniversary, Corvette LT-1, STARS AND STRIPES BABY (with a really bad bimini)!!!!!!**
* Footin' anyone?
RON PAUL FOR PRESIDENT
"It is no coincidence that the century of total war coincided with the century of central banking" - Ron Paul