My advice is: learn Flex focusing strongly on MXML, or learn Haxe.
AS3 is verbous, unexpressive and unproductive compared to those two.
edit: you can check out the AS3 cookbook. nonetheless, after rereading your post, I've come to understand, that your problem is not learning AS3, but you're rather having design problems. Am I correct?
edit2: "Is it uncommon for people to work in pure AS3?"
I wouldn't say, it's uncommon. I'd say it's even common, i.e. a common mistake. Why? It's inefficient. I think, I can tell, because I did that a lot.
the main role of pure AS3 is to create libraries and frameworks. To create actual apps, it is really the hardest way one can choose. In all handmade apps, GUI turns out to be the most time consuming part. Laying out GUI using code is a nightmare.
Now MXML is really great for normal GUIs (a graphical editor is even better of course). And the Flash IDE is great for creating funky animated things. The best thing you can do with AS3 is take ASWing and their GUI-editor. As nice as ASWing is, its ugly and a pain in the arse to skin. But, you can.
The advantage of Haxe is, that its a more powerful language than AS3. You effectively write less code, and its signifficantly more typesafe, so you run into less errors and spend less time debugging. Also, another advantage is, that you can use the same language for creating a serverside backend for the app and pass objects transparently to it, using Haxe remoting, which cuts the transport layer down to nothing. All validation and business logic can run both on client or server. Plus it's open source and it evolves very fast. AS3 was a great thing when it came, but it has stalled eversince, which is nearly 4 years now.
So while there's nothing wrong using pure AS3 per se, you always have to compare it to the alternatives. Pure AS3 is inefficient and for geeks. Flex is highly efficient. Haxe is more efficient than AS3, and is for the really cool geeks.
