If Wal-Mart pays higher wages,it will help attract better employees.
I can give a couple examples: Costco is known for better pay and benefits than Wal-Mart. In my experience, the employees at Costco are at a much higher level than the Wal-Mart.
Chick-Fil-A vs. McDonalds
Chick-Fil-A is known for paying a few dollars above the hourly minimum wage. The quality of the employees, and the customer experience is much higher at Chic-Fil-A than McDonalds.
This is only one step for Wal-Mart. The management will need to follow up by making improvements in inventory management by making sure the stores are adequately stocked with merchandise, and by making sure enough employees are in the stores to service the customers.
If Wal-Mart tries to make up the cost of increased wages per employee by scheduling fewer employees in the stores, then it will result in angry customers and the move will backfire on Wal-Mart.
I think the savings will come in attracting better employees and reducing employee turnover and the recruiting and training costs associated.