if you want to do a true fuel service on the car, you need to do the whole fuel injection service, adding a simple bottle of seafoam isnt going to help, also the car isnt new, if its the stock engine, its wear and tear, build up, 28mpg isnt that bad

 

Ignition timing correct? Cam timing correct?

 

it just had the timing belt and water pump replaced, so they should be correct