Whats a good framerate to have?
I don't know if the current AH version looks any different, but in the past I always felt as if the game was stuttering if framerates ever dropped below 45ish. If you fly around and most of the time framerates are pegged at your monitor's refresh rate (60 for me), then they might not sag too far when you get into a fight. And that's the most important for gameplay, how far the framerate sags in a fight. Sagging below 30 is unacceptable in my opinion, and below 45 it felt like the teeny tiny stuttering would affect how well I could aim and maneuver against the other players. Some people are happy with FPS sagging to 20 occasionally, but for me anything below 30 meant I would immediately go to the settings menu and turn down some options, and I'd aim for 45 fps or higher for almost all of the time even in fights.
If I couldn't run framerates that high, then I'd save my pennies and buy an upgrade of some sort. AH doesn't change hardware requirements all that often and they've left in lots of graphics options you can turn down or off, so even lower end hardware can still get you pretty high framerates. You just lose some of the graphics eye candy, that's all. But I figure if you're playing the game just for the eye candy, there are lots of boxed games that look better than AH so you can fly them to get the absolute prettiest graphics. If you want realistic planes and the AH gameplay though, there isn't any realistic alternative right now.