To answer Rumbletiger’s original question, the spell’s description says the simulacrum has half of the original subject’s level with the appropriate feats/skills/etc and thus would be able to craft anything the original subject could have done at the adjusted level; with the same corresponding limitations. Therefore the simulacrum CAN cast spells/craft items requiring the expenditure of XP provided it does not lose a level to do so.
The same applies to Greenleaf: yes, a Druid Simulacrum of at least 9th level could be ordered to Awaken an animal/plant (expending 250xp apiece).
Presumably such expended xp could be replaced via a variant of the indicated complex healing ritual as means of maintaining its existing level since this would not violate the spell’s statement it “it can not INCREASE its level or abilities”. However the implied 100:1 implies most “depleted” crafters would simply be replaced with another fully experienced version whenever possible.
[Question: Since such a ritual is deduced rather than stated, would applying the follower/cohort rules under the Leadership feat supersede?]
Regardless, such use of a simulacrum definitely reduces (and in many instances removes) the PC’s direct involvement in the crafting process, since the simulacrum merely needs instructed what to craft. Likewise, it could aid the PC crafter directly by applying second-hand feats, skills, and/or requisite spells which would otherwise need outsourced; as well as providing the Aid Another modifier.