It looks ugly but translate should work. Try (untested):

//userprop[nameprop="Version" and contains(translate(valueprop,
                                   "ABCDEFGHIJKLMNOPQRSTUVWXYZ",
                                   "abcdefghijklmnopqrstuvwxyz"),"v1.1
+")]
[download]

I'm not sure why you would want to lc the static string.