Aldo Applesauce revolves around issues of fitting in and adapting to life in a public school, with a secondary theme of vegetarianism adopted because one does not want to kill animals. If these are not themes you feel important to share with your children, as is certainly true for me, there would be little reason to read the book. Add the "typical" family with its fragmented lives, a brother and sister who have little involvement in each other's lives, and the values which are accepted as normal (young girls' interests in boys, clothes and rock music, a 4th grader who goes many places on his own etc.) and I am left with no reason to want my children to read this book, at any age or stage.
It is only fair to mention that there IS, in the friendship between Aldo and DeDe, an acceptance of each other's oddities and a developing place of trust. While this is an admirable concept, there are, in my opinion, other books far more worthwhile that include that theme.