Let me start by saying, your plug-in worked perfectly, as advertised. I gave you full stars and selected works as my vote for your plug-in. However, I found part of your plug-in which could have been easier to use, without doing too much additional programing on your behalf.
I would recommend handling the exclusion of posts & pages similar to the way you handle the exclusion of categories.
I would even go as far as saying, the page & page structure should be easily identified, so you know exactly which pages are and are not being included..
It may be just as easy to add a check box next to the Categories, Posts and Pages in there respected areas within WordPress. Then go back to your Plug-in's admin area to build the sitemap.
It is extremely difficult and time consuming to find the post/page id, especially if you install this plug-in after your WordPress site has been in production for an extended period of time.