Final answer:
Product cost most affects buffet-style restaurant menu planning due to the significant impact of menu costs, which include resources used to change and manage pricing. Staff salaries and competitors are also relevant, but less directly influential to menu planning.
Step-by-step explanation:
When planning the menu for a buffet-style restaurant, the most influential factor is Product cost. This is because menu costs, which are the costs firms face in changing prices, play a significant role and can be impacted by the cost of products. Menu costs include resources spent on analyzing market demand, updating sales materials, changing billing records, and revising product and price labels. Additionally, the economic environment and consumer expectations about price stability can affect the pricing decisions and strategy for a buffet restaurant.
Other costs, such as staff salaries and competition from local competitors, are also relevant but do not impact the menu planning process as directly as product costs. Salaries are a fixed cost to some extent, while competitors might influence pricing strategy rather than menu planning. Economic projections may indicate longer-term trends but are less applicable to immediate menu planning.