Good rules to live by, though it is possible to be overly cautious. You may (or may not) find that the improvements that Sublime Text brings to your productivity are worth handing over a little bit of control.
In reality though, whether it's closed-source or not tends to be irrelevant - the Gnome (3) project is a good example of what can happen when an entire project changes its mind on how things can be done, to the dismay of its users.
Yeah, but the source of GNOME 2 is there, and the people who are not happy with ver.3 created several forks. They may or may not be of better quality, but they are there and if on wants to continue living in GNOME 2, (s)he can do so.
The situation is not exactly the same with Sublime Text... it is completely at the mercy of its creator...
In reality though, whether it's closed-source or not tends to be irrelevant - the Gnome (3) project is a good example of what can happen when an entire project changes its mind on how things can be done, to the dismay of its users.