I wouldn't change the game engine anything for this project! My initial question targets my games that might come in the future.
The second game is already in production and will be announced in the next weeks. I have a large collection of different video game concepts and I selected something I can create at the same time as Galactic Crew. Since the engine is the same, I instantly had everything from basic game features, settings, UI controls, input management, asset management, pathfinding, state machines, etc. It wasn't much to add before I had a playable mock-up. The main work of the second game is done by freelancers (2D artists, screenwriters, level designers, etc.). This way, I can manage both projects at the same time. I also wanted to start a second project while Galactic Crew is still in development, because it will make sure I can continue my work next year! Like most Indie games, the sales of Galactic Crew declined in the first year. If I want to continue to make games next year, I can either abandon the game and start something new or need a second source of income. I expect the upcoming Steam Sales to be as good as the last ones (the numbers are pretty constant), but this won't be enough to finance an entire year of development after I paid my taxes (they are pretty high in Germany...)!
As one can clearly see in the Steam discussions, I care about every single player and issue. Bugs are normally fixed within hour if possible, almost all requested features were added within the next two updates and so on. I also get a lot of very positive e-mails from players who enjoy the game. It isn't done yet, but I improved the game and its engine dramatically over the past 10 months and I will continue my work.