I've been using WebStorm lately and have been considering purchasing it but I'm also learning Scala on the side and would also benefit from IDEA. If IDEA can handle NodeJS and TypeScript is there a point to purchasing WebStorm as well?
I'm currently working my way through the Functional Programming in Scala course on Coursera using Eclipse. I'm not sure if I would make use of IDEA for now which is why I'm unsure whether to buy it or save myself $70 and get WebStorm only. Plus I think WebStorm currently supports TypeScript better than IDEA but that could change with an update.
I'll definitely pay the $99 if they throw in WebStorm. Is that something you've heard JetBrains has done in the past?
That said, for general use I really like the Scala support in IDEA. I'd suggest playing around with the free version a bit - as you mention, Play support is only in Ultimate, but the Scala plugin itself works fine in Community. You can get a feel for how IDEA manages projects, handles debugging, that kind of thing.
First, the easy ones. ReSharper, dotTrace and dotCover are all independent products that don't really overlap with the ones I'm about to talk about.
The "Core" doesn't exist as a product, but it's all the things that are product-independent and aren't provided by plugins like the editor, HTML/CSS/JS editing support, debugger, theming, etc. I'm mentioning it because each IDE ends up with a slightly different version of the Core based on when it was released, which means that using IntelliJ with the Python plugin might not have all the features of PyCharm if PyCharm got a major version update more recently than IntelliJ.
WebStorm (JS/HTML/CSS IDE) has the core functionality plus Node.js plugins. You can install other plugins, but only a limited subset.
AppCode (Obj-C IDE) has the core functionality plus product-specific Obj-C plugins that you can't install in any of the other IDEs. AppCode only shares a few plugins with other IDEs, like the Vim emulation.
RubyMine, PhpStorm and PyCharm have the core functionality plus language/platform-specific plugins for Ruby, PHP and Python respectively. You can install other plugins, but nothing that would turn one of these into the other, for example installing the PHP plugin in PyCharm.
IntelliJ IDEA has the core functionality plus a huge variety of Java plugins. It can also use the language-specific plugins from WebStorm, RubyMine, PhpStorm and PyCharm as well as others that are downloadable. It can install almost all of the plugins that are supported on the platform - the only exception I'm aware of is Obj-C support.
Hope that answers some questions.