Telephoto-conversion lens

Not really. First off, the zoom on teh SP560 is pretty impressive, the 35mm equivalent of 27-486mm. I can't imagine needing more than that, even in Nepal. Then there's the fact that a teleconverter will magnify the images coming into your lens by about 2. The downside is, that this will cause your camera to have to be compensated in it's exposure settings because of the loss of light by 1-2 stops. And depending on the quality of the glass in your teleconverter, you may also run into clarity issues. You will certainly run into some "barrelling" issues at the extreme end of your focal length. this will make the image look like you're looking out of a barrel. This can also happen with wide angle converters as well.

To be honest, while you can purchase these options to screw onto your existing lens, I don't recommend them because the trade-offs involved simply outweigh the benefits in my mind.