but this definition of "malice" appears to me to take the word "malice" rather too far from conventional English usage for usefulness in communication to others.

You are mistaken. I provided the standard English definition, correcting your somewhat misleading usage. Maliciousness refers either to taking pleasure in the thought of someone coming to harm or the deliberate intent to do said harm.

Reference to google: define confirms this. The exhaustive list of non tautological (that more than simply refer from 'maliciousness' to 'malice') is as follows:

• Of, pertaining to, or as a result of malice or spite; Deliberately harmful; spiteful
• maliciousness - malice: feeling a need to see others suffer
• Maliciousness - Malice is a legal term referring to a party's intention to do injury to another party. Malice is either expressed or implied. Malice is expressed when there is manifested a deliberate intention unlawfully to take away the life of a human being.
• wanting to cause harm or pain to another

Basically it is about one of intention, desire or taking pleasure. Other usages (if there are any) are far more obscure. This is good because we need a word to refer to having a reduction in someone else's utility as a terminal value and 'spite' has somewhat different connotations. Spammers only interested in advertising their products simply do not qualify. 'Evil' would be a legitimate word in the context.