Are booking agencies becoming irrelevant? Yes...
Interesting article which I agree with for the most part. The ubiquity of social networks has really afforded comics a direct way of harnessing an audience. I now it's easy to snigger at a comic who quotes how many twitter followers they have as some sort of stamp of quality but it does provide a decent metric of how popular a performers brand is which can be key to gig rate negotiations. On that note I also found an article on this topic a few years back which I feel is suitable supplementary material which you can read here.
Furthermore, the articles overall argument that a comic can truly "go it alone" has some even more practical options like funding your own promotional materials. Since no one starts at the top of the bill I'd always advise mocking up a couple of extra hand-outs and the like that highlight future appearances alongside general contact info. You'd be surprised how effective something like that can be. For those interested this place does cheap flyer printing alongside other stuff but you should still shop around to find the best deal for you.