Is there a point to leveling Spell Totem?

I don't seem to see what changes when I level my Spell Totem support. Now it is level 7, and it still has a 250% mana cost, still has the same duration, and still does 40% less damage. Besides increasing the requirements, what changes with leveling, what am I not understanding? Thank you.

It does gain duration. And life I think (tho I may be wrong here, perhaps it's the attached gem's level that determines life), hopefully someone else will answer that.

http://en.pathofexilewiki.com/wiki/Spell_Totem

The duration increases.

The level of the Totem created on based on the level of the gem. Level 1 Spell Totem will create a totem based on a level 31 monster level (the level requirement of the gem), while a level 20 Spell Totem gem will be based on a level 60 monster level.

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Qarl wrote:

The level of the Totem created on based on the level of the gem. Level 1 Spell Totem will create a totem based on a level 31 monster level (the level requirement of the gem), while a level 20 Spell Totem gem will be based on a level 60 monster level.

Does this mean the totem has armor, evade, and a base health value that increases as the totem gem level increases?
Does its critical strike rate/damage go up, does it gain resistances or anything else we should know other than duration?

Most spell totems seem to get killed long before their duration runs out, so it'd be nice to know what we're actually getting.

While we're on the topic of why do you level gems up, what is the reason for levelling detonate dead?

Higher level totems do seem harder for mobs to kill. I was also really liking the longer duration for my skeleton totem.

As for leveling Detonate Dead, leveling it increases the damage from the corpse explosion but also the mana cost and stat requirements. I only use it to clean up corpses so I keep my Detonate Dead at level 1.

A totem's cast speed, crit chance, crit multiplier, etc are based off of your character's stats. If you have a 10% crit chance with a spell then so will your totem with the same spell.

Hmn maybe I haven't noticed the duration change, particularly because (if the link is accurate) there is no change between level 6 and 7.
By the way, I also use increased duration on both my spell totems, my skeletons (which gives me a longer-lasting totem AND longer-lasting skeletons, and reduced damage doesn't seem to affect the skeleton'S damage, but I can't test that) and my spark (which gives me longer-lasting totem AND longer-lasting sparks, they fly forever...).