Unfortunately I cannot provide much in the way of support when it comes to third party products….for Widgetkit Pro, I’ve never used it myself so I won’t be much help. However, your two options as you presented are possibilities, but before you try any one of them, I would make sure you have a backup of your site using a backup plugin at least because backing up with the standard WP method doesn’t save everything. The least would be to make note of your slideshow settings, and also copy each slide and captions in a text file in case you had to re-enter them.
Whatever works out for you, it will be interesting to find out how it goes for you. Check Widgetkit’s documentation as well and check their forums out…I did find this but although it’s for updating, it might work for upgrading too (maybe)