You dont HAVE to... but you should replace them in pairs. Out of four, if you still have two that are fairly decent you can postpone their replacement for awhile. Just make sure the tires of equal wear and tread-depth are are paired together.
The 2004 Toyota Highlander has 16 valves.
You don't as it has a chain not a belt.
I own one and have Michelin tires on it, with which I am very happy. They may not be the least expensive tires on the market but you get what you pay for.
The 2004 Toyota Highlander is a gas-powered vehicle.
The 2004 Toyota Highlander has a 4-speed automatic.
The 2004 Toyota Highlander has an inline 4 engine.
The 2004 Toyota Highlander is 15'5" long.
The 2004 Toyota Highlander has a 27 degrees angle of approach.
The 2004 Toyota Highlander has a 21 degrees angle of departure.
The 2004 Toyota Highlander has double overhead cam (DOHC).
The 2004 Toyota Highlander's turning circle is 37.4 ft..
The height of the 2004 Toyota Highlander is 5 ft. 6.1 in. (66.1 in.).