Today, I finally turned it over and opened the back to see how it was constructed. There are individual springs, so at first I thought it was 8 way hand tied. Upon further inspection and research on web, I think it is a drop in spring system. The wood frame looks like 2x4s you would buy at lumber store. I don't know how to tell if it is the hard wood, but it is not pressed wood. It has dowels, a corner wood support, and is glued.

I am debating about getting a new sofa or reupholstering this one. If I get a new one, I am going to go with a higher end brand like Henredon. Now that I have seen the inside, I am leaning towards putting this one in the basement, but not reupholstering. It has value in that it is still comfortable, but appearance wise, it not suitable for living room anymore. ( Normal wear and tear)

Still, a new sofa is expensive, so I would appreciate some opinions.

Based on your description you may end up paying more to have the set redone than you would buying a new set. Most sofas except those in the high end range last 5-7 years based on industry averages so I think you have got your money's worth.

Had it been a high end group in the first place I might opt for reupholstery but I don't think I would for a mid range set.