wi-fi can be more secured than wired networks due to the fact that few companies encrypt wired networks or have client/port authentication mechanisms to grant access. Even though WEP is a weak encryption, access is still granted based on the client having some shared key for access. The challenge for wi-fi is bandwidth. The radio spectrum environment causes the access point to behave more like a hub than a switch although companies like Xirrus are working to correct this fault. This means that behind an AP the link may be 100Mbps the wireless clients are sharing that single connection to the LAN. I see wi-fi as more of a convenience and cost savings on cabling architecture right now until the radio spectrum can be made to work more like the switched wired environment.
A lot of security issues are actually actually better answered after determining what the networks are to be wired for. For example, you can put a WPA2-Enterprise security key on a wireless network, but sometimes, the administrative access to access points is handled in an unecrypted way. This is the same scenario for network cameras (a camera sends encrypted data, but the text used to access the camera’s interface as admin is unencrypted).
There are all sorts of vulnerabilities that you will face, so it’s important to establish external protection. What I mean is secure the heck out of the lines coming into the company because you even decide on LAN or WAN.