As far as Hawaii diving, it has good diving as long as your expectations are correct. It's about the fish and critters, some unique scenery, and the opportunity to dive with big stuff if you're lucky. I definitely do miss the corals and color when I'm there but it is what it is. Even though Hawaii diving doesn't excite me in general, some of my most memorable dives have been there. I personally would not make a trip to Hawaii just to dive. But if I'm going to be there anyway, which seems to happen to us every 4-5 years for family or business reasons, I'm certainly going to dive. One of the bonuses of diving in Hawaii is that the land is so good, it's great to combine land and diving. I think the reason to do the KA is not that it's outstanding diving or the worlds greatest liveaboard destination - but if you're in Hawaii for more than a week and want to dive and do land stuff, well it's just a heck of a lot more convienient diving than doing dayboats.
As far as the Kona Aggressor, or any liveaboard, you can't make any assumptions on what the passengers will always be like based on who happens to be on it one week. But, I've never experienced a real party crowd on any liveaboard even if passengers are younger. (Actually, some of more party inclined have sometimes been the older folks...) It varies but people are mostly there to dive, so people do tend to get up early and crash early. If people are up later maybe they're having a glass of wine and chatting or watching a movie or reading, but never partying and draining the bar until 3am.
KA is a nice boat, nice size. When we were there a lot of the crew was new, but things were good. The DMs would have benefited from more experience. The food was outstanding, due to a combination of a very good chef and the ease of provisioning they have in Hawaii compared to more remote or 3rd world places. The food was better than most of the restaurants we ate in on land, actually, and we try places from the local places that have good reps, to very upscale, and anything in between. The diving is remote for the Big Island, we went all the way south where the dayboats don't go and there is practically nothing to be seen on land but lava flows. They may not have gone that far south your week if conditions sucked? I'm not sure how divable it is if they went around the tip of the island to the other side. Yes, you can get wifi and cell coverage on the boat in some areas, you're close to a well connected island with antennas sitting up on volcanoes, it's not nicknamed the cell-phone-Aggressor for nothing.