There are many Websites that are ranking on top of google in spite of a poor Page Speed, which begs the question, If the Page Speed parameter worth glossing over. Here's the thing, you Page Speed comes into play as a competitive advantage wherein you're struggling to outdo your competition and have necked up on all or most other fronts like KW targeting, Onpage Optimisation, Link Building etc. There are hundreds of optimisation techniques which are directed to get better of your competition, Page Speed is just one of them, which is in our control, have definite outcome to judge in terms of various page rendering and of course is easy to implement.
But surely you need to weigh your options when it comes to invest your time, effort and money in optimising your page speed.
Hope that helps
Amit