When adding a second connection (i.e. a wireless connnected system adding a wired LAN connect) the client system should determine costing of both routes to the destination over each NIC to determine which NIC to send traffic out. This is all based off of the TOTAL routing costs of each route to the destination and not just the local interface metric.
So what you are most likely seeing is the wireless route has a similar or lower total routing cost as the wired route to the resources which you are connecting. One item you can do to trigger a route change is to set the route costs at the router port for the wireless LAN to a higher number than the wired routes. As an example, set the wired routes to a metric of between 1-4 as you need and set wireless routes metrics to between 10-15 as needed. This should drive most traffic to choose the wired route over a wireless route. You will need to diagram out routes to resources and the costing of each router hop to determine flows.
NOTE 1: The default routing metric on the Windows client is the automatic metric. The automatic metric is based off of reported network speed of the NIC.
NOTE 2: I have seen where the wireless NIC driver will initially (and erroneously) report that the connection has the maximum theoretical speed generating a very low metric which is never updated. Update your NIC driver first then if not resolved open a case with your vendor for an updated driver to resolve.
An explanation of the Automatic Metric feature for Internet Protocol routes.
TCP/IP Routing Basics for Windows NT.