The cameos to me made a lot of sense. Everyone that had a cameo would have been involved and needed to be shown. Bail Organa was part of the rebellion from the start. It would have been weird for him not to have been there helping make decisions. There's no way Red and Gold leaders would have sat out such an important mission. C3-PO and R2-D2 were definitely on the Tantive IV in ANH so why not show them with the rebellion? Tarkin was basically the highest ranking officer in the Empire. Not only would he have wanted to be personally involved in the progress of their most important weapon, he was in charge of the thing in ANH, so it's nice they explained how the lead up to that worked.
I think if you just kind of let yourself get caught up in the feels it's easier to let the movie entertain you and carry you along. Just my 2 cents.