How useful are negative level effects for players?

We all know how painful negative levels are when we ourselves get afflicted with them. Especially at low levels, facing energy draining creatures can be quite a challenge.

I'd like to turn the table today and say: 'Don't ask what level drain does to you, ask what you can do to leveldrain!'

As a reference, from the pathfinder SRD:

Some spells and a number of undead creatures have the ability to drain away life and energy; this dreadful attack results in “negative levels.” These cause a character to take a number of penalties.

For each negative level a creature has, it takes a cumulative –1 penalty on all ability checks, attack rolls, combat maneuver checks, Combat Maneuver Defense, saving throws, and skill checks. In addition, the creature reduces its current and total hit points by 5 for each negative level it possesses. The creature is also treated as one level lower for the purpose of level-dependent variables (such as spellcasting) for each negative level possessed. Spellcasters do not lose any prepared spells or slots as a result of negative levels. If a creature’s negative levels equal or exceed its total Hit Dice, it dies.

The most accessible way to inflict level drain on enemies would be enervation or its big sister, energy drain. The lich even gets a semi-passive level drain aura: Eyes of the Bodak.

Now my question: How useful are these spells in practice? And how do they compare to spells of the same level?

I'm currently playing a lich, and energy drain is right up my alley. I would love to RPly build a bit around that.

But even if we assume best rolls, the effect of a level 9 energy drain (-8 levels) would be, as far as I can see:

• 40 hit points lost -- okay, nice, but a martial does more in a single round (if they can connect)

• -8 penalty on ability checks -- I don't really see the practical benefit. The dazzling display spam from the Vavakia Vanguard should be affected (intimidate check), but they roll so high -- in the 50s -- that a 20% penalty would still mean that most of my party would not manage their saving throws. Athletics would be affected and put a penalty on how quickly they can climb out of a pit spell. But eh?

• -8 levels on spells: OK, so drain doesn't remove prepared spells, the spells just become less effective, e.g. with a view to penetrating SR and saving throws. But again, if we take end-game mobs with 30+ levels, -8 means that they are still over most HD caps. Their spells might fail to stick more often though -- enough to justify the effort?

• edit: I forgot the -8 to saving throws. This might indeed be a nice boon for us; -8 is significant for most enemies. Still: worth it?

• The obvious negative level spam. But at 30 levels, it would still take 8 maximised enervates to down an enemy. Not really efficient.

I'm sure I'm missing something. Is there a way that these effects are useful for us players?