I have a 1 year old Innova G 2007 model and my interior was still clean.

Like OTEP has said I don't drive with windows open, I maintain cleanliness and vacuum it weekly.

I don't use seat cover because I like the moquette seats of Innova G, in fact only after a year that I decided to have it Interior Detailed not because it is too dirty but I wanted to have a better smelling interior.

The interior sidings are easy to clean...its hard plastic I use cloth wet with dish washing liquid and then wipe dry with MF cloth.

Why worry about interior clealiness when you can have your car send to a detailer to make it feel like new again