I'd have to disagree with "significantly" improve.
F.lux
As interesting as this app was for me on Android I didn't care enough about it to keep it installed.
F.lux was never available on Android, as far as I know. The developers wrote a long blog post about the complications of porting over F.lux to a rooted version of Android. You may be thinking of Lux instead, which overlays a reddish filter over the display, rather than integrating directly like F.lux does. (It's been some time since I was reading about them, but the conclusion was that F.lux worked definitely better -- and differently -- than Lux.)
Biggest benefit of F.lux is visible not during daylight or sunlight, but when you're in bed with your iPhone or iPad and some warm ambient light shining down on it. With F.lux, the display is warm and matches the ambient light. Without F.lux, the display is a jarring white-blue that can mess up the way you sleep.
The blue-white makes the display look perfectly white in daylight, but when it comes to a "warm" lighting environment...
That being said, if you've used unjailbroken devices with the default screen all of your life, then you've probably gotten used to the harshness as "normal" and the immediate "yellow" effect of F.lux is jarring.
Jailbreaking iOS 7 is not a good idea, things that ppl don't realize ... until it happens.
iOS 7 runs slow enough, jailbreaking it is gonna be catastrophic. Everything is written for and loaded on to MobileSubtrate. The more that's loaded on that extension, the slower it gets over time and you can forget about loading Winterboard for skinning and theme'ing a new look for iOS 7. I would just manually change all the icon by replacing all the png files, but that's as far as anyone should go.
You'll see more stuttering, lag and massive batt drains on top of the current iOS 7 performances across the board.
F.lux was never available on Android, as far as I know. The developers wrote a long blog post about the complications of porting over F.lux to a rooted version of Android. You may be thinking of Lux instead, which overlays a reddish filter over the display, rather than integrating directly like F.lux does. (It's been some time since I was reading about them, but the conclusion was that F.lux worked definitely better -- and differently -- than Lux.)
On the iPhone 4, it runs slow.
Android slow.
The kind of slow where you can start typing a message, set the phone down, then watch all the letters appear on the screen several moments later.
Yeah, that slow.
Jailbreaking always seems like a good idea, but the jailbreak app store/marketplace is a MESS. Finding the right jailbreak has always been difficult for me. It just has never been a smooth process. Although I agree with many of your points, at this point, I really like iOS 7 as it is, and nothing annoys me enough to want to sift through the jailbreak market. Not worth it.
Just need BiteSMS for some sort of quick reply as well as f.lux I can't really say there's much more else I would need.
I refuse to go to iOS 7 because of no quick reply.
I never sift through the Cydia store, so please stop this behaviour right now.If I need a specific tweak for a specific problem, I use Google to find the exact tweak that would provide the solution I need.
For all else, I use the jailbreak tag on iDownloadBlog. They cover every single tweak that's genuinely decent.