Gillespie didn't do anything again, and it isn't as though Kaspa looks particularly frightening of late on this tour.
Macgill has had success against England in the past although granted not so much on the last Ashes tour. It's pretty obvious England still look suspect against this type of bowling and I wouldn't just wait for the Old Trafford and Oval tests before bowling them both together.
I think the greater turn of Macgill, combined with his good googlys might have a shock value. Like Warnes slider it way well cause alot of problems because it's a delivery England aren't used to since Warne doesn't bowl it.
The two of them also have had good recent success when operating in the same side. Even if one doesn't fire, invariably the other one has a very good match.