Aces High is a great game. But look at this thread for a minute, and you'll see why it's so difficult to "fix" it. I see people arguing that the game needs to become more hardcore, that it needs to be less hardcore, that it needs better graphics, and that the graphics are fine. There's a million ways to "fix" this game, but many of them are directly at odds with one another.
After awhile, if you play something enough, you're going to get bored. Building a strong community is helpful, but the friends I've made in Aces High I wound up playing with in other games too - Drex and I played World of Warcraft and Star Wars: The Old Republic together, and I've played Diablo III with Grizz. The relationships here transcend the game, and thus won't solely save it. When I got together with Drex for dinner a couple of years back while in Oklahoma City on business, neither of us had set foot in an AH arena for years. So there's that.
I will say that the I've always had two major issues with AH that I think make it inaccessible to newer users. One, it lacks an easy user interface; the one it has is functional and actually pretty powerful, but it's clunky and unintuitive. A lot of new players are going to get lost and give up before they even figure out how to map buttons and enable their controllers. And second, the game needs a game primer for new players - not a tutorial on how to fly, per se, but rather a tutorial system on how to fly in Aces High. It's okay IMO to throw people into the meat grinder, but it's not okay to give little guidance on how to start engines or what different field maps, sides, fuel multipliers, and the like mean. Aces High did a great job of serving as the natural evolution for Air Warrior and Warbirds, and back then these sorts of facts seemed obvious, but now the new players come from completely different backgrounds.
Just my two cents. It's still a great game, and I hope it remains successful far into the future.