How are they two separate issues? If you don't go as fast as possible, you can get less work done before your deadline. Even with today's CPUs and the kind of parallelisation that a good DAW program will do, I still routinely see producers (myself included) hit CPU usage limits. In audio DSP, programmers have responded to the increase in CPU capacity not with higher-level languages but instead with more computationally expensive algorithms (modern filters, for example, use techniques derived from circuit simulators for solving nonlinear equations).

Besides, actually writing the DSP code makes up a comparatively tiny portion of the development time. Tuning and tweaking the DSP algorithms takes far more, and designing the user interface dwarfs both. I know multiple audio products which use Lua for their UI layer because the productivity increase is so significant. And there, you don't have to worry about performance to anywhere the degree you need to in the DSP.