From someone who spends a lot of time sore, I would have to somewhat say yes, you do need to be sore.
Simply, you get sore when your body does something it is either 1)unaccustomed to, or 2) an activity it is accustomed to, but at a unaccustomed intensity. I think if you are really...and I mean REALLY...following the principles of progressive overload then I think you should spend a lot of time sore.
I do however think nutrition, sleep, and training frequency also play a role. You don't want to do too much, eat too little (or not enough protein) or sleep too little. You gotta train hard AND rest hard.
I think people's bodies react differently too though. While Diane Sue may work out just as hard as me, maybe her body is just better able to deal with DOMS, I don't know. Sometimes I think the more muscle you have, the more predisposed you are to DOMS. Kinda makes sense, in that if you have more there to hurt, well......
Jeez, if I don't do IMAX in a month or so, I feel that brand new lock-up in my calves like I hadn't done it in years. I can take 2 weeks off of kickboxing and when I do do it, feel like a Mack truck hit me the next day. So...it doesn't take long for your body to "forget".
I wouldn't rely on the presence of soreness. BUT, I would track my weights to atleast make sure I am trying to increase every time. That is a really hard thing to do when you work out with videos. One of the biggest drawbacks IMO. Discipline yourself to do it if you have time, because after a while it gets frustrating not being able to remember your poundage on all the tapes. I work out at lunch with 3 other people, and we only have 1 hr max, and since Cathe tapes are all about that long, I have no time to spare. But, when I lift gym-style, you bet I know the poundage and I write it down and always try to progress next time.
Just my thoughts.......
Janice