Re: Lacking conviction and/or motivation?
Sounds like burnout. I used to write novels myself until the sheer difficulty of ever becoming published and thus being able to share your work with people and have it reach beyond friends and family single-handedly killed my passion, even though it's obvious Hollywood could certainly use good and original plotlines right about now.
To me, it sounds like you need a clean plate and a fresh start. That sci-fi novel series probably got too big, complex, and too deep to manage, and after a while, you just couldn't take it anymore and you were getting worn down from it. Usually a lack of motivation is a sign that it's time to move on, and the spark of creativity and passion that used to drive the urge to keep it going burnt out and it was a sign to start over with something new.
Writer's Block is the #1 murderer of stories and projects, but it's mainly because it occurs when the writer has already accomplished all the things they really wanted to do with the story and the rest is just ho-hum stuff that they feel they're obligated to do to finish what they've started and give the project closure. This is also why I don't plan ahead very much. It's okay to have a faint game-plan for the future of the story, but don't outline creativity. I have tried outlines before and holy cow, I almost always go against them and throw them out anyway. To be creative, you just need to be dynamic and let things go in different, unexpected directions. A journey is simply a boring commute if you already know the way, but when you head into the unknown where anything is possible and surprises lurk around every corner, that's where it becomes a real memorable adventure.
So yeah, I think you just need to appreciate that sci-fi series for what it was, remember it in your heart, remember all the good times you had with it, and move on to give yourself a break, let the slate be clean for a little while, and then dream up something new and intriguing.