I have a similar setup to some neighbours. Only I have enabled the guest zone with a password and MAC filtering, so only those I rely on can use it.
I have the same router as you (DIR-655) and use traffic shaping (Advanced -> QoS Engine) to make sure my computers have first priority on the net; after all, I'm the one who's paying. To give your computers fixed IPs, you can "reserve" IPs to your own MAC addresses. That way I never experiences any limitations while others can use the full capasity when I don't use it.
The Guest Zone blocks access to your own devices and shields you from being hacked. Note that a good hacker can always overcome such blockings. You can also use Access Control (Advanced -> Access Control) to limit what others can do. You can also block traffic based on web addresses and such. Just play around with the advanced settings.
I know that others have said "Be careful" about this, but I just wanted to repeat it. Except exposing yourself to possible hackers, you could potentially lend your network to some pretty nasty people.