Unfortunately, right now, we don't have a RenameItem method. The approach to use now is similar to what you are doing now. You will have to delete the current item using DeleteItem now. You can then add new folder items using UploadFeatureSetTask or through setting the outputAnalysisItem parameter for the actual task to the folder item with the new (renamed) item name. Sorry that this is the only way to do it right now.
That is a good suggestion. If you can, I suggest that you submit any enhancement requests you think might be useful to the Esri Ideas site at http://ideas.arcgis.com/. Our team then tracks these requests and then decide whether we should include the suggestion in a future release. Any ideas are definitely welcome!