True, the IDEs are poor, for a certain definition of poor. Had I not used IntelliJ for Java, for example, I'd find IntelliJ for Scala amazing. Knowing how much better it can be spoiled me, but frankly, IntelliJ for Scala is not bad. It just could be better. Also, Emacs has a very robust Scala mode.
True, there's a lot to learn before you can consider yourself fully fluent. You do not need to know everything, however. And once you've started on the path, things tend to flow naturally. For example, implicit conversions are easy to grasp. Once you understand them, implicit parameters and type classes are not much more complicated. Once you know type classes, it opens the door to a lot of functional "design patterns" - functors, applicatives, monads... these are not strictly necessary, but they're fun to learn about. And they teach you algebraic data types, which in Scala means case classes, sealed traits, ... it all sort of flows naturally.
True, it's easy to write absolutely un-maintainable code. While that's true of any language, Scala makes it rather easier than most. It's also very easy to write highly maintainable, legible code, and to avoid complex, ascii art based operators (or at the very least to offer wordy equivalences at 0 cost through `@inline`). I feel that saying "it can be hard to read, if you don't follow basic guidelines" is a bad reason not to use a language. A good reason to be careful, though.
My personal experience is that, once you start feeling comfortable with the language, you get much more productive than with Java. It does require some initial work, though: if all you know is OO, learning how to design your code for composition rather than inheritance takes a while - it takes a while just to realise that it's not a bad idea, let alone embrace it!
Also, ScalaCheck. Man, do I wish there was a good Java equivalent for some of my legacy code (that would not require me to rewrite all of my tests).