Do you have the J series V6? If so, it looks like the timing belt has to be replaced at 105,000 miles, while the other models have timing chains that don't need replacement for a lot longer... but that could be wrong, it was a quick google search.
If your car has a timing belt, you need to replace it when the manual says so. If the belt breaks, your engine usually breaks as well. If you are replacing the belt, it is a god idea to replace the water pump as well. That is because you have to do a lot of labor to get to the belt or the pump, and they are in the same spot. Doing both at once costs basically the same as just doing one, while ding them seperately costs almost twice as much- it is all labor cost, not parts.
I had a 2007 Subaru Impreza, and replaced the belt and pump at 100k.
Lastly, spark plugs should be done, but they should be very easy to change... and cheap. I wouldn't pay that much for the service, but it probably depends on your location. I paid $600 for my timing belt and pump change, but that was in Indiana (low cost of living), on a different type of car. Now I just own cars with timing chains instead of belts, and will do the work myself when they are due.