Are expensive speaker cables worth it?

No. For any sane run length, adequately gauged copper (16AWG to ~25ft, 14AWG beyond) is electrically transparent — resistance, inductance, and capacitance all land far below audibility, and controlled listening tests have never reliably distinguished properly made cables. Spend the difference on speakers, a sub, or panels: parts of the chain where measured differences are enormous. Buy tidy, well-terminated wire and move on.