I think we engage in an awful lot of what amounts to mental masturbation. It's a lot more fun to imagine a project, think through the details of it, pick stacks, come up with domain names, etc. than it is to actually do the work. This is human nature. People do it all the time in all sorts of ways.
What seems to help for me is:
1) Stop trying to keep up so much. The New Hotness may change constantly, but a lot of that is just self-promotional noise on the interwebs. I've heard that there are still something like 30,000 VBA programmers out there (and they're very highly paid!), but you never hear about them, because it's completely unsexy. We read awesome blog posts by one-in-a-million developers and automatically compare ourselves to them, and it's a recipe for disaster.
2) Clearly define your project goals, meet them, and move on. It's so easy to allow feature creep or refactor-obsession to happen.
3) Time management techniques like the Pomodoro Technique. This has helped me immensely. I break down projects into tasks and estimate the number of Pomodoros. I make a mark for each expired one, and it becomes obvious when I've started over-obsessing on pointless BS (which happens a lot).
4) Endless to-do list. When intrusive thoughts and ideas pop into your head, write a summary in your to-do list and move on. You don't need to check if MyAwesomeDomain.com is available right this second, so put your idea on the list. How many of us think of the cool domain name and either get completely derailed, or tell ourselves "I'll just remember that for later!" and proceed to waste far more time later trying to remember WTF that clever idea was?
5) Unplug. It's sooo hard to just turn the computer off in the evening and sit down to read a book, but it helps quell the racing thoughts better than anything else I've found. The single worst habit I have is jumping down a tech rabbit hole, then relentlessly pursuing it until I've either solved it or literally start to fall asleep at the keyboard! (I bet that's a common experience here)