I agree with using power line devices as an easy fix, as long as they are on the same phase and don't have to cross any in-line power conditioning devices they should be fine.
The signal propagated from access points is best suited for receivers parallel to the antenna, so, by placing an access point on each floor level connected by power line devices you will be able to provide a good signal across all areas.
As for wireless extender/boosters, don't bother. unless you spend a large sum on a multi radio device (NOT the same as multi antenna) the extender will cut the transmission rate by 50% immediately as it plays the listen then talk game.
That 50% applies to the poorest signal between any two points in the chain.