How much faster depends on your connection speed and the speed of the hosts your downloading from. Pro connects to up to 10 hosts and Basic connects to 8. So the potential is there for faster speeds. Pro also connects to more peers 5 compared to 3 with Basic, so you can get better search results.
Whether it's worth it or not seems to be a matter of opinion. You probably won't see a big difference unless your on a really fast connection, but you should see some difference(if your on dial-up you won't see any difference). I have Pro and I like it and the money helps to develope new versions of limewire
.
If you get Pro your files will be safe because they are not stored within the limewire program. They are in a folder outside of LW.
Hope this helped. You can find more info by using the search in the upper right of this page
.