As you mentioned you are a relative rookie with DSLRs, my advice would be for you to keep the 40D and practice more. The 40D isn't a bad camera at all... and you have some decent lenses. I'd suggest a bit of a shuffle with lenses (details below)
I have the Canon 15-85mm (my most used lens) - and it's great as a 1 lens solution - for both travel and landscape. I have the Canon 70-300mm L which pairs with it great for a 2 lens solution (if you want more zoom). It appears you also have the Canon 70-300mm nonL and the 70-200mm L non-IS. I would recommend that the 70-300mm L is a much better solution than those 2 telephone zoom lenses that you currently have. The 70-300mm L is sharper than both, has a great 4 stop IS system and true fast, accurate USM focusing. So it beats the best of both your telezoom lenses (as 1 lens!)
If you sell both your 2 telezooms, you might be somewhat out of pocket - but you'll have a better lens: an L lens that will last you a lifetime for any body. [Mine is very sharp at 300mm f/5.6] AND it's a much more practical / portable solution. (I believe you can use your Kenko converter on the 70-300mm L - which will focus in good light / high contrast, or at least it does on some bodies, maybe also the 40D). And it might work particularly well with the new dual pixel LiveView AF - which apparently can AF at smaller apertures, eg f/8 to f/11.
Another thought (after that) that I had is you might want to look at getting the Sigma 8-16mm UWA... which is the widest non-fish eye zoom lens currently available for Canon APS-C DSLRs. It would work so well complementing your 15-85mm. Getting to such extreme wide angles can be challenging, but also fun. Again, this lens is a great companion for travel. (PS.. I dislike the 50mm f/1.8 - but I did have 2 copies of that lens in the past).
The 70D would be a reasonable upgrade to your 40D, but practice and technique are more important than having the latest / greatest gear. Though definitely the 7D and 70D have advantages in handling, and some features, the 40D would probably not be your main limiting factor at this stage. The 70D will eventually come down to lower prices (I think Canon has been reasonable with the 70D price of $1,199 USD). You can already get good deals on the 7D, but if I were in your shoes I'd wait a while to upgrade your body.
Hope this helps.