It depends on what your focus is. If you are a "Web Applications" developer, that is different from being someone who primarily designs marketing pages. There are several categories of web pages. In fact we could probably have an entire thread just debating what those categories are. But I break them down this way.
Pages that provide a service - ex: Quicken.com, online banking, various internal apps (hr, timekeeping, etc) (Web Application)
Pages that provide information - ex: CNN.com (Web Information)
Pages that sell something - ex: Amazon.com, bn.com (Web Store)
Pages that are of a purely marketing focus - ex: gijoemovie.com (Web Marketing)
*Note I'm not talking about interactive or not, just the purpose. Yes there will be some bleed over, and some sites that do more than one.
I find that Flash is generally good for 2 and 4, moreso than 1 and 3. Yes there are exceptions, I'm sure there are flash developers out there who can point to a good app page built in flash, just as I'm sure there are good MVC or Ruby developers who can point out very "flashy" information page built with nothing but some JQuery. I've personally done some of both.
What languages you know is a function of what you want to build, and who you want to work with. While I advocate knowing many languages, there is something of an artists touch to any flash application. In my experience, you are better paying an artist for that, just as (in my experience) you are better paying a developer for the technical details of your major web application.
As a developer, I would treat flash as I treat Photoshop. I can open up photoshop and make minor changes. I can change colors, slice, optimize, and make minor adjustments. I cannot open photoshop and design a page from scratch. Similarly, in flash I can open it up and make minor changes. I cannot design a pretty flash application from scratch.
You also asked specifically in the context of getting a job. To get a job you need to be
- Really good at the primary skills
- Functional and serviceable in related technologies.
If you are a generalist at everything, or claim to know everything, you won't stand out, and people won't believe you (it may be true, but people still won't believe you). You need to impress your potential boss that you are good at his primary need and that you can "get by" at secondary needs. About things like flash I generally say "I'm not a designer, but I know enough to work with them."
If you've never worked in the field before, then it's hard to give advice beyond that. A career primarily in visual design is very different from a career primarily in development. It's hard to be sure which you want without being in the trenches some first. Be willing to learn new technologies and change if you are not happy where you are.