While I could see similarities between Wall Buddy and Wallpaper Man, I think Wall Buddy had its own unique feel, as Regularshowman mentioned. Wallpaper Man was just a story Benson came up with in order to try to stop Mordecai and Rigby from wanting to purchase stupid things/hire people from T.V. all the time, and it didn't even work, anyway. It had a Halloween vibe to it, making it more enjoyable than anything else. Not to mention, the other park workers had major appearances, something only Mordecai, Rigby, and Benson had in Wall Buddy. I personally thought Wallpaper Man was meant to be more humorous, too, providing comedic relief instead of a valuable lesson.
A similarity between both episodes was one of/both of the main characters wanting to purchase something from T.V. However, I just saw that as typical Rigby behavior, and really didn't think about how it may have related to Wallpaper Man. I think Wall Buddy was supposed to be a wake up call for those who don't like to clean up their mess. It had its funny moments, but honestly, I thought there were more morals than humorous moments.