There are plenty of non-mesh aircraft out there that look really nice, and cross sim borders fairly decently. And get the Ban Line and Parcel Hud as flying without it is like russian roulette, with it though you can cross the mainland without trouble.
As for ban lines themselves, they go up to 80m I think, just fly over them, and you should be above them anyway so as not to be a nuisance to 'ground folk'. Again the Ban Line hud will show you when you're above them. The only ones that go right up to the ceiling are where you've been selectively banned from a parcel, which will usually be your fault.
So, if you are going to fly above people's property, try and keep at least 100m above them. If you interrupt their party with a big noisey engine you will probably find yourself on the ban list next time. Some folks are fed up with aircraft for just this reason. Some even place orbs with a 0 second warning to deliberately de-rezz your aircraft - I prefer the ban lines
Sky junk is prolific in some areas, we have no right to tell people what to build. I do mention to people (in a friendly manner) that sky junk is a pain and forces us to dip under it (never above or around!) thus bothering folk on the ground sometimes. I've sucessfully elevated several skyboxes this way to a sensible height.
Also bits of wall and cars hovering in the air are always worth mentioning as many people forget they left them there and are glad to get rid of them to get their prim count down.