I'm getting close to finishing a PhD in applied mathematics (next May), and I'm starting to think about next fall's job application season. I'm realizing that one of the things I'm missing is a strong recommendation from a senior academic that isn't on my committee or a professor I've taken courses from. I realize that it takes time to cultivate these relationships, but I'm now also realizing that I've been a fairly introverted student in the sense that I haven't really pushed myself to build any collaborative relationships that would make asking for a recommendation more natural. I've had lots of conversations with senior people at conferences or who have visited my department, but I never seem to follow up because I doubt their level of interest in me or my projects (this is flawed, introversion-driven reasoning, I realize). I have a few loose collaborations going with other junior academics but again, I've been a little shy and flaky on pushing those projects forward for some reason or another. I also wouldn't consider these collaborators senior leaders in my field, which isn't an issue for collaborating, but the value of their recommendation is perhaps less so than someone higher up the proverbial ladder.
The question is the following: since I still have a little bit of time before the next application season (6 months or so), should I focus on nurturing the collaborations I already have going, or should I start trying to get a little more bold with more senior people? I realize that I should probably do both, but I welcome any input.