I am thinking of making summons less a waste of a spell slot - maybe this idea could be developed/explored further?
We currently have an Animal Companion code that scales the animal companion based on a pet "caster level" from 1-50. I've played with Animal Companions, and although they lose effectiveness very badly in event server (due to getting Morded mostly), overall the scaling seems rather appropriate.
Hence, why not implement the same scaling function for all the (currently) useless Summon spells (Summon Creature, Create (Greater) Undead, (Epic) Gate, etc...)
To make a dedicated summoner more useful, and open up other building options, we could re-purpose the following feats:
Augment Summoning - Makes summons/Animal companion immune to dispels (especially Mord's). This will help keep the Animal Companion relevant in high level areas.
Mirror Golem and Mastery I-III are changed to Summoning Mastery I-IV. Open this feat line to other casters (Nature/Divine/Bards/Warlocks).
At baseline, all summons will start with a " very low" value for HP/AC/Saves etc, and the exact value will depend on caster level.
Summoning Mastery I-IV pushes these values upwards (how it does so TBD).
To make the Summon spells actually feel more powerful when casting a higher level one, the type of creature summoned and potency of its special abilities (e.g. a skeleton is crit immune, a fire elemental does fire damage) should also scale with the exact summon spell being cast.
Although a scaled summon can be very powerful, getting a decent one would require significant investments in feat and caster levels.
Characters are limited to 1 summon at a time anyway, and cannot spam them. This also stands as a replacement for a Golem or an alternative to the Shadow Simulacrum rather than an addition.
You still need to burn spell slots to cast the summon, and spontaneous casters will have to give up spells known to learn summons should they want to summon.
Being a spell, re-summoning a new creature should the old one die overcomes the issue with Golems being a waste of 4 feats once it goes down. This makes it advantageous over a golem, which loses its effectiveness past Server 2 due to their re-castable nature.