Further questions:

• Are you happy with how close you can come to wildlife with the camera you have now?

You have a f:3.7 equivalent of a tele that goes to 420mm in film speak , with Image Stabilisation.
To get this for a dslr, you have to spend a lot of money.

The Sigma 70-300 can come even closer (and you have more megapixels, meaning you can crop even more) but it has no image stabilisation, and it needs more light at 300.

• why a kit? Why not a body with what you really want? Just a suggestion (always very difficult to make): why not get a body of a 40D and for example a Sigma 50 or 105 f:2.8 macro lens? And use the panasonic for the moment for tele?
  And then, when the money allows,  get a real tele like, for example, the Canon EF 300mm f:4.0 ?

Yes, a lot of money. But it'll give you what you need, and it has Image Stabilisation.

Sorry, but in my opinion the Sigma zooms in that kit are not a step ahead when you already own the Panasonic. My idea.

There are no Borg. All resistance is fertile.