Actually, many child stars had their parents benefit and then leave them with almost nothing. Not saying that this is happening to Jessica because she is technically not a child, but IMO, the one person who will always have your best interests at heart is yourself. True, Joe might be better than some stranger, but I don't think he always had her best interests at heart. He was always after the money.
Also, I think Jessica was the one who benefited the most from the marriage. First, she was PUT ON the map because of Nick. Their relationship started when 98 Degrees was still hot (they met when she opened for him at one of their concerts). Then after she broke up with him, she started fading away again, which I think is partly the reason she got back together with him again - to create media attention. No one cared about her before her linkage with Nick and this started way before they got married. I also agree that this was the reason they didn't sign a prenup (because Nick was worth more than her). It is true that by the time they got married 98 Degrees was going downhill. However, they still had songs out that were pretty popular because I remember a few about Jessica. As for her, I hardly remember what songs she had out then. SHE WAS NOTHING! The show completely catapulted her to superstardom because everyone wanted to know what went on behind the scenes since they were the first "Hollywood" couple to air their lives on national TV. As time went on, her stupidity, whether real or not, made her more popular than Nick, who wasn't as entertaining.
Therefore, I don't see how Nick benefited at all. The show was the beginning of the end for him IMO.