Ask yourself the following before you press the shutter:
1 - Is it a good location?
I'm quite familiar with that location so I'll mention some specifics: the Longfellow bridge is a beautiful view in person, but there are 2 flaws that make it tough to produce a compelling photo. (1) It's a narrow bridge, roughly a quarter mile long but the sidewalk is 2 feet wide. So your options for composition are very limited. (2) You're about a half mile away from land, with a lot of water and sky in the way, so it doesn't always lend itself to wide-angle shots. In general you want to get as close as you can.
In addition you want to make sure everything in the frame is something you want in the frame. It doesn't really apply here since the view is nice, but if there's a big ugly water tower or boarded up building in the way, that may not be something you want.
2 - Is it a unique location?
As you said, it's postcard pretty. Meaning everyone who comes by wants to get that shot. And since the bridge is so narrow, everyone is taking the exact same picture. And in this case I do mean as similar as you can get. Try taking a shot from somewhere people don't always do it. If you can get on a roof somewhere, that's great - everyone else is stuck with the same perspective at ground level. Or if you can figure out how to make a location that most people skip work for you, that's even better. For example, if there's a fence in the way, get right up to it and shoot with a wide aperture to hide it.
2.5 - Is there something unique about the location RIGHT NOW?
All that said, you can make a great shot in a cliché location by being in the right spot at the right time. People have taken a trillion shots of the moon, but if you get a silhouette hot air balloon or bald eagle right in front of it, that's pretty cool.
As far as a skyline goes, are the buildings lit up a funny color for a sports team? Are there fireworks? Are the Blue Angels flying overhead? These are just a couple ideas.
3 - Is the image well-composed?
You should always be asking this, but just a refresher - is everything that I want in the image, actually in the image? Is there anything in there that I don't want in there? The good thing about cityscapes is you usually have time to recompose, try again if some ugly tourist hat pops up in front of you.
In this case, the boats are really nice - they add some interest to the image. On the other hand, that bird in the top middle is distracting.
4 - What's compelling about the image?
Last, why are you taking the picture? You have to ask yourself is it just a nice snapshot, or are you trying to show something. What's special about this that I'm taking a picture of it? Do the colors look special at sunset, is there motion that you can freeze, or can you add motion by using a slower shutter speed? There's nothing "wrong" with a snapshot, but generally there's no artistic intent in there. What's your intent?