Well networking can get confusing fast. Bridge could provide performance increases but I wouldn't say it's anymore/anyless secure. You'll basically have double firewall and NAT, making it nearly impossible for any inbound traffic to come in. This will surely limit gaming and P2P traffic (even things like instant messaging file sharing) as you won't be able to accept any connections from the outside.
Typically speaking, you want to avoid having more than one router/NAT/firewall/DHCP server on a home network as home network devices aren't designed to allow for this.
If you want though, you could totally isolate wireless by connecting it's WAN port to a LAN port on your modem. However the laptop won't be able to communicate with the desktop at all, but should be able to access the Internet fine.