Spade author here!

My probably controversial opinion on output code quality is that if you have to see the generated Verilog, I've done something wrong since there is probably a compiler bug if you need to go down to that level.

Of course, you could just be looking at output from tools like timing reports, and then as someone else commented out, it is a bit of a tooling issue. Spade does emit (* src = *) attributes which yosys and friends accept to show the original Spade source instead of Verilog, but it is still kind of leaky in some cases