Welcome to our online forums! To answer your question, it is recommended that you update your Slingbox and the applications just so you do not run into any future issues. Also, there are minor bugs that were fixed with the updates. There is not a way for you to stop being asked to update your software/ firmware.
Below are a couple links with information on the updates.
If you have any further questions, please do not hesitate to reply.
Sling Moderation Team