If you are looking at Intro, then you've probably already scouted through the features of Live 8 and maybe even glimpsed at Live Suite?
Intro for me is perfect for actually learning how to use the tool. I downloaded the Live 8 trial and spent a month playing around. I didn't manage to use any of the features that Live 8 has that you don't find in Intro.
So for me, it's worth the investment to learn the product and the good folks at Ableton will discount the price of Intro against any upgrade you make should you outgrow this version.
The only thing I would say is that it retails on the Ableton website for a lot less. Play's partner on this page is not offering a very good deal at all!