using a wire brush is a definite no while the intake is attached to the head, if a steel wire gets loose or broken inside the intake will cause damage to the piston, rings or cylinder - so forget that.
there are something like 4 nuts attaching the intake manifold to the head, imo just take it out and clean it, otherwise if it's not choked (that would take a lot of buildup) leave it and do it next time you remove the manifold, not worth the risk imo for the probably minimal gains.