It will also depend on your cameras ability to auto focus with an extension tube at that distance - I cannot say how it would perform. You can of course focus manually but that may not be easy either with a DSLR.
See how much sharper the images get when I use the 60mm. The shots taken when I use this lens are usually 1-2 feet away which is quite nice distance for insects. Not to close - not to far.
You could always get some cheap tubes and have a play using your zoom lens. I think the results will not be great but you can get a feel for it.
The next step would be a macro lens of 90-100 mm
Having said that I remember using my 12mp DSLR with a 90mm macro lens. The auto focus was so slow I had to use manual focus. That made shooting slow an focusing difficult. It so much easier with my new camera and with the addition of flash.
This sort of photography is quite tricky and you get a lot of dud shots but I get a lot less than I used to.
Shot with the 60mm
Bumblebee on Buddleia by
Paul Stickley, on Flickr