The spark plugs are under pencil coils located on top of the two valve covers. The cover under the wiper cowling is somewhat exposed because the intake manifold is off center whereby it droops more over the other valve cover near the radiator, thereby covering those pencil coils.
So, yes, the intake manifold must come off if you want to change out all six plugs. The job isn't too bad for an experienced shade tree mechanic, but might be best left to the professionals for others with less experience. There are a number of electrical connections that must be undone/redone (some single lock, others double lock), as well as various hoses and a few brackets, all of which need to be refastened correctly during reassembly. There are also certain torque settings that must be used not only for the spark plugs, but for the intake manifold bolts themselves; and the intake bolts need to be tightened in a certain order.
As regards changing them every 30k to 50k miles, the manufacturer's service schedule says 100k, so that is what I plan to abide by. And while I would love to tackle this job myself, I will be leaving it to the pros.