If you're hitting the park regularly, dedicated park skis are absolutely worth it. They feature twin tips—both ends curve up—so you can land and ride backwards (switch) comfortably. They also have symmetric shapes that feel balanced whether you're skiing forward or backward, making spins and landings much more natural.
Park skis are built tougher where it counts. They have thicker, more durable edges that resist cracking on metal rails and boxes, plus reinforced bases that handle the abuse. Regular all-mountain skis will get chewed up fast on rails, and their edges can crack or pull out entirely after repeated rail impacts.
They also tend to have a softer flex pattern, which makes pressing, buttering, and popping off jumps easier and more playful. If you're just cruising through the park occasionally, your regular skis are fine. But if park riding is your main thing, dedicated park skis will perform better and save you money in the long run.