Tying to LotM's post in the last thread--unfortunately the bonuses do not depend on ownership, but rather on the Location Keyword (LocTypeInn, LocTypePlayerHome), otherwise it defaults to the lesser spell. My suggested solution was :
1) Script the Bed itself
2) OnActivating the Bed, set a variable to '1', and register for Sleep
3) OnSleepEnd, check that variable equals 1 (just to make sure it's got the right bed), and wait 3-4 seconds
4) remove the Rested Spell, and add the Well Rested Spell.
5) Set the variable to 0
You get both messages this way (assuming you add the WRmessage), but it should work reliably from what I've tested.