Are expensive knife sets worth the investment?

If you cook regularly, yes, with a caveat. One excellent chef's knife will outperform an entire budget set. Premium knife sets are worth it if you use most of the included knives. The real value of premium knives is longevity: a Wusthof or ZWILLING set, properly maintained, lasts 20+ years. Budget sets typically last two or three years before needing replacement, making premium knives cheaper per year of use.