Are the standard techniques of DSP still relevant to modern signal processing applications?
Linear Time Invariant (LTI) operations, filtering being one of them, whether IIR (Infinite Impulse Response) or FIR (Finite Impulse Response), are fundamental to DSP. 

A few people who create DSP systems today do so without 'getting their hands dirty' with that 'low level stuff' by dragging and dropping higher level components on 'system builders'.

Much as I, a dyed-in-the-wool low level DSP man might bemoan that trend, it's not much different to the fact that very few people today write assembler, we all use higher level languages. Myself, I don't write assembler now, only use C when I have to, but for preference stay in Python. 

It's just so much more productive to design at a higher level. But this move into higher levels of abstraction in software is only possible because of the speed of computation targets makes any code inefficiency due to generation from a high level irrelevant for many purposes.

While power constrains DSP applications, and many of them are hand-held and battery driven, most practitioners of the art will be using low level tools, designing FIR filters by the stage and the bit, to optimise power. When (if) the power constraint lessens, then more design will move to a higher level. But it will still be 'compiled' in some way to use LTI primitives at the core.