I agree the spider image is a bit soft. I found it a very difficult subject - not much colour variation and so small it made it very difficult to get a good focus on - my nasty cheap tripod didn't help much either.
The Kenko tubes cost about A$180 landed on Ebay which is significantly cheaper than a good macro lens.
The 75-240  was a kit lens with an F80 that I bought a couple of years ago - fairly average lens.
Will have to do a bit more research on the difference in macro & telephoto lenses - all a bit techo for me at the moment
Thankyou all for the comments so far 
