I've wanted to contribute more to open source but I felt like the best way was to contribute to projects I use myself. When my company switched to Angular three years ago, I contributed a few fixes to some Angular UI libraries, but then my company decided to develop their own UI library so I became more removed from OSS ones like ui-bootstrap.
Also, my expertise is more generally web app development; I don't have a specific technical area of expertise such as kernel development, graphics, or compression coding theory. As you said, I could potentially be useful building a web site for a project like GNU Radio. Not that it wouldn't work, but it seems most sustainable for me to contribute to a project that I use. That would be projects like Babel, Gulp, Browserify/Webpack, Angular; those guys are so huge it's not clear they really need any help.
Oof, sorry for the long response time - I somehow missed the notification on this comment. Also, Go Hokies! =)
And yeah, while I would love for you to help with GNU Radio (we need it), like I said in the post, it's really only sustainable if you are making contributions to a project you care about.
I will say that just because a project is large doesn't mean they don't need help. Taking GNU Radio as an example, we have hundreds of developers in the commit tree and still struggle to get this stuff done. Now, the projects you listed are somewhat different in that they are web projects, so the chances of them needing help with web stuff is much less. That said, based on quick glances, both Gulp and Browserify look like they have gaps. Both of them, for example, have their docs principally in the form of giant Markdown files (here is Browserify's). Browserify recommends this web app, "Browserify Search", for finding compatible packages, but the tool appears to be gone. The last demo on Browserify's examples page, "2D Velocity Control", is broken for me (running latest Firefox). And are there other web apps you can think of that might be useful to the Browserify community? Debug tools, perhaps? Is there such a thing as a tool that would unpack what Browserify is doing for any given webpage that might be useful to other web developers?
Anyway, I'm kind of taking shots in the dark, here, because I'm not a web developer and frankly have no idea what Browserify does, but I would bet there is still opportunity, there, to create something new & useful and contribute to the community.
Your fundamental point, though, I agree is true. It is going to be more difficult to find ways to contribute to some projects compared to others - especially in web development.