Once upon a time if a vampire hit you, you could kiss goodbye to 2 levels and wghts could take away 1 level.
This made these creatures feared. Now apparently energy drains are badfunwrong due to player entitlement and they ahd to go away. However I am willing to compromise.
Bring back energy drains a'la 1st and 2nd ed but do not make the level loss permanent but have it last longer than a few rounds. 24 hours minimium, out to something like a month. So you have the effect which is still scary, do not make it permanent and the negative levels can be removed via restoration spells and whatever other mechanics they can thnk up.
No permanent loss of levels, no xp loss. Collect enough negative energy levels though and you die and depending on the source say hi to a new wight/vampire/spectre.