Diversify your learning
I believe learning should not be like how a not-too-informed investor trying to maximize profit in stock market. He/she may only dump all the capital in the most potentially lucrative stock and then feel all the fear of "having made a wrong choice." Instead, learning should be optimized and diversified. No usual people can only learn one thing for 100% of the time and not bored to death. You'd need to get out from this paradox of choice before you can feel better about your learning time investment.
A book read is a book read, the things you have learned (and more importantly, assimilated into your preexisting knowledge base) cannot be taken away. Depth is certainly important, but don't overlook the occasional serendipity sparked by knowledge across multiple areas. Who knows someday you wouldn't be able to make learning software easier by recasting it as a fantasy story? And who knows if a software you write to analyze the text structure of your favorite fantasy books will not be applicable in other areas? Knowledge should not be in different silos, they should be mixed, and variety is certainly good.
I don't know much about software industry, but I'd think perhaps using 40-50% study time just to keep up with the ever-advancing trend and technology in software, 30-40% to expand into relevant fields that would facilitate your work in upcoming 3-5 years, and 20% just to learn anything that interests you. This should be a good starting point and you can calibrate that as you go along.
For the 40-50%, you probably know what those materials are. For the 30-40%, feel free to pick 2-3 of them as a starter. And if any of them seems not too relevant but interesting, allocate it to the 20% category. Meanwhile, set small attainable goals (just by simply adding a couple extra lines in your diary to document how much you read/done) so that you can see your achievement. Don't ever feel guilty about not learning the most, most, most important thing. The fact is, that thing can change day by day, narrowing it down wastes more energy than learning a couple more less important but useful things. And the difference? In the latter case you have still learned something, it the first scenario? Nothing but a lot of frustration.
Put external structure to your learning
Reading is certainly good, but it should not be the only format of self-learning. For learners who struggle to find motivation, incorporate other formats, people and organizations into your learning. Join a class, write a blog, listen to a podcast, post questions online, get onto a project, identify a mentor, etc... try to make your learning interactive, to keep it fun and to avoid procrastination.