Hopefully this question doesn't sound too dumb to the networking experts here

, but if I have my network set to filter MAC addresses - "Only listed MAC addresses can connect and DENY others" - what would be the advantage of enabling encryption, since performance will suffer? Also I don't believe there is one encryption scheme available on the DIR-655 that will work with my mix of b, g and N wireless devices, is there?
Devices on the network -
wireless:
2 desktops with 802.11b (one Win XP/SMC USB wireless adapter, one Win XP MCE/Netgear USB wireless adapter)
1 desktop with Win XP MCE/dlink Extreme N PCI adapter
1 laptop with onboard Intel wireless g (Win XP Pro)
occasionally a Sony PSP
wired:
Xbox 360
Sony Blu-Ray player
WD MyBookWorld network storage drive