Hello ????
1) If a graha is vriddha or mrita - karmic effects are very little or had been completed - does it still matter if these grahas have a good or bad laajitadi or deeptadi avasta? What happens during their dasa? the effects are very low? I'm thinking that it must be good to have malefics in mrita
2) Will the tara nakshatra effects get manifested if a planet is mrita?
Every planet has a job to do that we need done, if its mrita or vriddha it can't do it or it can barely do it to a not enough degree. These avastahs hav eto do with the planet manifesting their bhavas and the things they represent. The final stage of manifestation happens in the 5th level dasa and that is when this avastha is important in showing j ust how much of what the previous dasa levels in indicated actually manifests.