First off, it does seem to fit in with the occasional interpretation of 7th levels spells and higher being rituals rather than spells used on an adventure. What would be the point of memorizing Simulacrum? Without Reincarnate or Limited Wish, all it does is make a weaker duplicate of some being that is no better than a zombie. Animate Dead is much better at making zombies. Phantasmal Forces is better at duplicating appearance, if you just need to fool some people on short notice. Polymorph Self or Polymorph Other is very good for insinuating an impostor into the enemy's ranks. All of these are lower-level spells. Simulacrum thus seems intended to be used as guidelines for a multi-stage magical creation rather than a day-to-day spell.
Second: Simulacrum seems to have two main uses:
- Personal Assistant. When I first read about the spell, I thought of Mr. Atoz, the librarian from the original Trek episode "All Our Yesterdays". His duplicates have independent action, but limited independent thought, enabling him to do more work. Wizards who don't want copies of themselves could copy a favorite companion who has moved on to other things, or copy someone who spurned their affection.
- Long-term Subversion: Illusions and polymorphs work over the short term, but a long-term plan to control an empire may require duplicating a lost monarch. illusions are notoriously easy to dispel. Allies might not agree to being polymorphed and might betray the wizard, and Polymorph Self might end too quickly and prevents the wizard and the monarch from appearing together in public.
This kind of affects our image of what wizards are like. We would expect wizards to collect many body parts, not just for spell ingredients, but as an archive for later creations. They would routinely collect samples from enemies they have slain, or from clients as part of their payment. Part of their magical experimentation would be testing combinations of body parts to see what kind of creatures they could produce. They may have cages of failed experiments.
All of this is worth further thought.