From my point of view it's always very useful to learn native app development, iOS as well as Android. As you have already mentioned, the majority of companies are looking for native app developers, since they do not want to depend too much on external companies or frameworks, other than the actual developers of the platform (Android, iOS and so on). I also think, once you are capable of developing native apps, it's a way easier than using a framework like Titanium or PhoneGap. Furthermore it is always good to enhance your own skills and in particular native app development is a field, where you can learn a lot. Not just about the language but also about the architecture of the underlying mobile operating system. And in particular for Apple, I think it's crucial to learn to develop native. They have very good resources on their developer portal and there you learn also a lot about the intended user interaction design.
Last but not least, I would recommend you to go ahead with Swift. It is a great and powerful language, fixing many of Objective-C's weak points. You can basically start form scratch with Swift without the need of Objective-C. The complete Cocoa-API is accessible via Swift. But if you want, you can still combine Objective-C and Swift. For instance if you need to use a external library which is not implemented in Swift yet.
Hope that I could help you a little.
