It's been my experience that creative-minded people (myself included) are truly their worst critics... Not that there's anything wrong with that (to borrow a signature line from one of the best sitcoms of all time...), however. Honestly, I think judging your own work too harshly can be more of an asset than being one of those people that is totally in love with their own words. But one thing that I have noticed is that the former group can often cause writers to prematurely abandon ideas that have actual potential.
For example, I have accumulated well over 100 (probably closer to 150 by now) story ideas, and while a few of them are too terrible for me to ever share, I document them anyway. It's my sincere belief (as this week's quote from yours truly demonstrates) that most of the time a bad idea simply needs the love, devotion and development to be fleshed out into something worthwhile, and who knows, with some sculpting and polishing, that terrible idea that you were so ashamed of could end up becoming your best work.
I've experienced this first-hand. One of the many stories I'm developing (in my head, at least) began as an overblown, James Bond-esque spy thriller with action setpieces so ludicrous that Michael Bay would roll his eyes at the mountain of disbelief and lack of imagination necessary to conjure them. I'm happy to say I was 15 or so at the time and that the story is slowly turning out to be far more morally complex and layered than its original incarnation.
Anyway, getting back to my point, the idea is that writing is like sculpting. Nothing comes out as gold. Creative writing is a living, breathing thing, and like anything with a life of its own, it takes time to grow and mature. I've certainly seen that with my never-ending work on my first screenplay. So as ideas pop into your head, even if they're not related to your current project, be sure to jot them down. You never know when one of them might blossom into something special.