Having a water softener reduces consumption of salt and rinse aid hugely, provided your machine has an adjustment for the water hardness or can detected it automatically.
Very basic machines will use more consumables as they have no adjustment, but weekly sounds excessive.
I top up the salt yearly, and the rinse aid monthly, clean filter about once a month on a 5 year old Miele.
We don't rinse the plates and use dishwasher powder (Sainsbury's), which seems to work better and is usually cheaper (10p).
Check your manual but every one I've read specifically tells you do NOT rinse the plates, as that's exactly what it does on its first cycle.
I know it feels intuitive to rinse them but you're just wasting water, energy and time, and it shouldn't make any difference if the machine is working correctly.
You may also notice on the door of the detergent dispenser there are usually some slits, or a tiny area, so a small amount of the powder is added to help the initial rinse cycle, which doesn't happen if you use tables or capsule.