lenses: macro -v- zoom with extension tube

I've not done a lot of close up work - flowers in the garden - but hope to do a bit more soon. I want flowers (including with stamen closeup) and butterflys (including head & eye shots).

I recently read a UK magazine article illustrating some dragonfly shots on plants near water in a park. This paragraph caught my attention and made me think

"I shot these images using a 70-200mm lens fitted with an extension tube - this enabled me to work close to the dragonfly and still focus on it. I could have used a macro lens but a zoom gives more flexibility with focussing and composition."

I use a D90 and have 35/1.8 as well as 55-200 and 70-300. I have been considering a macro in the 60 to 100mm range.

Does anybody have views or opinions on the subject of zoom+ext -v- macro?