As far as surface area goes, we couldn't do without a dinette table for the laptop, jigsaw puzzles, card games, and all the misc. assortment of "stuff" it seems to attract.
Seats are a different matter though. Pretty tough to fit 4 adults on the cushions. The ends of the seats closest to the outer wall are just another place that attracts "stuff"...
We used to use a custom sized TV table with folding legs that I made for in front of our jacknife sofa. Worked great and for eating too. Then we replaced the sofa with a power recliner and had to lose the TV table. Maybe a good compromise would be smaller seats/cushions with a table top end that folds up when needed??
We both have back issues and don't sit on the dinette cushions for extended periods. Sitting upright is the issue, not softness of the cushions. The power recliner has been one of the best upgrades we've done. Oh so comfortable to get comfortable on for long periods, like watching TV or reading. :) I made custom side tables with storage below for it so there's a surface to put drinks and food on.