WELP, I hope you don't mind Kwaurtz but I'm deconstructing your post.
Size: Your signatures are way too big.
Size is nothing more than personal preference. I made signatures vertical, horizontal, large, and small.
Personally, the larger the signature, the more in-depth you can go with it.
Lens flare: Isn't really serving a purpose, right now it seems you are imitating J.J. Abrams and just adding it.
Lens flares typically add a distinction of light to certain images, used to create flow within a signature, but you're correct. The flares in these don't serve a whole lot of purpose.
Backgrounds:I'm noticing either a lot of nothing, or just pasting another image behind the actual render. Doesn't really look well, in most cases. This is something that I'm working on myself. A lot of the time some of the better signatures I've seen come from nothing but manipulating the image in various ways to generate the background.
This is also very correct. Color correction, blending, blurring, abstract images, etc. help distort the background without ruining it and giving it a different feel in comparison to a copy-paste sort of deal.
This is solid advice and highly suggested.
I found my favorite method of blending a render's image with the background is to make multiple copies of the render, spread them out evenly, get a proper blur setting, and make something like the bottom example.
Colors:Never mix a bold color, like the blue of your name, on a super dark background like that, not only does it strain the eye for your average person, but that text is big, and honestly, not that appealing on the eyes.
This, I disagree with. While it's important to keep in mind to not overlay blue or red text against one another, vibrant colors bring out signatures sometimes. I like mixing browns & pinks seeing as the dull pink mixes well with it, but again, all personal preference.
Also, take note that overdoing brushes takes away from signatures. Oh, and you should find proper renders that don't have white marks left behind.
Also, while I'm here, here's a signature I made about 2 years ago.
Here's a helpful site for renders/tutorials:http://www.planetrenders.net/http://planetrenders.net/forums/