Wasn't the original plan to bring back the parasites but writer's strike got in the way?-Revisit the "Conspiracy" parasites, and I would've liked to have seen Tryla Scott back as well.
After years being stranded it might be too much for him to just become the first officer?-Replace Will Riker with Thomas Riker. I think a little shake up would've been nice. I've liked the ideas I've seen over the years about that change. Will could've gone on to captain another ship and Thomas could've stayed on the Enterprise-D, rekindled his romance with Troi. Data could've moved up to XO which would've strengthened the Picard/Data dynamic from the movies, and that exists in ST: Picard. Tom Riker as part of the crew also could've led to some nice character moments for the crew as they have to readjust to him.
Yes for Sonya.-Keep Sonya Gomez around longer. Maybe go forward with the idea of her and Geordi becoming romantically involved.
Tomalak was a nice character but how much is too much? Well, having him in a few more episodes wouldn't have hurt.-Have Tomalak as a recurring villain
Never. TOS had it, it was cool long ago but no to mirror episodes in STNG.-Had a Mirror Universe episode or two.
The Borg was a cool enemy but using it more than few times would make the unbeatable enemy not that unbeatable. I'm happy with 'Q Who', 'The Best of Both Worlds' 1&2 and 'I Borg'.-Made "I, Borg" the last Borg episode for TNG. I like the idea I've seen of the Borg not having a queen. It worked for First Contact, and the actresses who have played the queen have all been good, but I was more chilled by the impersonal force of nature the Borg were in "Q Who" and "Best of Both Worlds."