Just the addition of magic to the game already adds complexity to the base system.
Base system - the only pluses and minuses are advantage/disadvantage. Add in spells and we have, Guidance, Bless, Bane etc.
That was my point. The spell system already loads enough complexity on to the system that I absolutely think you could toss in a lot of additional things without notably upping the average complexity. Hell, you could probably do that and make it simpler if you went to a build-a-spell system with common components, but we all know most of the base would have apoplexy at that.