Shiny Syndrome: Another great story idea?

I'm writing a novel.  I'm really thick into it, about 55K in words. Then I have this dream, one with a really great appeal, which would make an even better novel than what I'm writing now.  Should I abandon my story for a better one?

No.

First of all, most "brilliant" ideas sound terrific, but by the time I get into them, I realize there's something missing.  Sure, there's probably a lot of potential in the idea oinking around between my eyes and my ponytail, but without enough marination time, it's not ever going to be dinner-worthy BBQ.  So even if it is better than what I'm doing now, unless what I'm writing actually sucks, I'm better off sticking to what I'm working with.

Secondly, there's the "Shiny Syndrome."  If I fly off after every shiny new idea I have, I'll never finish anything.  Magpies don't get published.  I frequently have ideas for possible novels (That night wherein I had three distinctly awesome dreams comes to mind: The power to turn dirt into water is pretty darn awesome, right up until you're in a desert and almost drown yourself. An outcast cat-man from outerspace seeks to reintegrate into his society by finding another man's missing daughter in the midst of a power crystal shortage.  A kidnapped alien being experimented on by other alien scientists gets rescued by a blonde bimbo too stupid to work her own spacesuit, which happens to make her invisible.) They all sound great at first imagining, but even a few hours leaves me throwing most of them into the mental slush pile.  If they're still good months later, they get moved to the "possible, when I finish what I'm working on" pile.

Just because an idea is good, doesn't mean it needs to be written.  I'm fairly confident that someone, somewhere, somewhen, will eventually write those plots (who wants blonde bimbo and the invisible spacesuit?  Going once, going twice...)  Therefore, I don't mourn the ideas I don't use. 

The only exception is when I'm working on something I finally have to acknowledge actually is terrible (and yes, I admit it, that's happened.  Abandon ship!!!)  Then it's back to the drawing board.  After all, it's not like I have a giant pile of stories just waiting to happen...

What do you do with terrific ideas that pop up when you're busy writing something else?  Do you file them away?  Note them down?  Hand them off?  Are there any you plan on going back to, one day?