I think Richie should join Ash because with his pokemon - Sparky, Rose, Zippo, Happy and Cruz (Pikachu, Taillow, Charmeleon, Butterfree and Pupitar) respectively would be a good, if not a valuable addition to the group if he was to travel with them. He will also have a new set of clothes as well as eventually becoming a permanent character in the story - Ash, Richie, Brock, Benji and an original female Pokemon trainer would be there also, but no more than five people can be in a single party at any one time.