First: it's good to see people going into pixel art. It's a great medium and a whole lot of fun too. I'm answering your question a bit directly here--I really don't mean to discourage you, I just think you're not taking the easiest approach here.
One important factor here is that the original sprites are making simplifications which work well at a low resolution but do not at a high resolution. Look for instance at your interpretation of his hair; with no offense to you, it's clear that you're kind of just copying the forms without really understanding what the original artist was conveying, and it doesn't really work. Some study of anatomy and lighting would definitely be beneficial; you don't need to do anything as drastic as a professional artist would, but take some time to look at some pictures and do some real life observation. Take a look at things like head shape; your guy there has a very square forehead, not much like what you'll see in real life.
Lower res sprites also often cheat on the perspective--you can get away with it, and it's more important to look good and be readable than to be technically correct. That does not work quite as well at a higher resolution.
Animations also won't translate nearly as well, in part because the framecount is too low for a larger sprite. If you look at the LPC sprites I had to do 8 frames in the walking animation for it to look decent (I might possibly be able to get away with 6 now that I'm a bit better at animation but not less).
On an even more general note, higher resolution pixel art is also a lot harder and a lot more work, so it's much less suitable for a beginner. I'd really recommend starting smaller.
I can't say that I really agree with you, Surt. There is a big difference between a request and a demand. "Would you consider tweaking the licensing to deal with this weird issue so I can be 100% sure that I can use it in my game" is completely different from the more aggravating type of "I need this but all animated and in 32x32 resolution for my game, no pay but you can put it in your portfolio" 'request.' Even a straight up license-alteration request ("Any chance you'd be willing to CC-By this so I can use it in my project?) isn't unreasonable as long as you're polite about it. It's also not unfair to assume that people are unaware of OGA-By (unless they're a well-known FOSS creator or OGA regular like you). Frankly, the DRM clause of CC-By was not properly disclosed and hasn't been well known for long. And most artists really aren't aware of the intricacies of FOSS licensing issues.
I would note that Bart might be able to relicense Sara's design/sprites under OGA-By. I don't know what rights he holds exactly, or how in touch with Mandi he is these days, but it's a distinct possibility.
I personally like OGA-By a lot, I've put it on everything I can of mine. As Saliv said, I don't think anyone will get upset as long as you approach it tactfully, which I have no doubt you will.
Thanks for letting me know--I was wondering what was up, but he didn't seem to care to say. I can understand that, a guy's gotta prioritize after all. I definitely haven't been able to do very much game stuff at all in the past several months :(
What's Clint up to these days? He's obviously alive, but I haven't seen him in this neck of the woods for quite a while. I hope it's the good sort of busy, anyway.
I think the tentative consensus is that art and code can be treated separately for this--all that needs to be released under -SA are direct derivaties of the graphics. That hasn't been tested in court, but as far as I am concerned it satisfies the license requirements for anything I release under the license.
Note also that most (or all?) of the LPC base assets (at least those made by me, Sharm and Charles Gabriel--I don't know for sure about those done by Beast or Daniel Armstrong (Hughspectrum)) are dual-licensed to CC-By. Of course that does not apply to any derivatives made by others, though they are free to dual-license as well if they please.
All that to say: you can absolutely pay me if you want. I accept large wads of cash, precious metals or gemstones.
Thanks for the additional information. I don't mean to be a bother, but could you please remove the woman then? The low res and edtis don't remove the copyright issue with using it, and we want to be sure that all the assets here are completely unencumbered license-wise.
Acidius: I'm glad you're willing to share so much of your work. However, a lot of these seem to have limited usefulness for most game projects, and a number of them (eg, this one, http://opengameart.org/content/opening-of-birs-cage, and http://opengameart.org/content/flying-bird ) really don't need to be multiple submissions. It would be helpful if you could combine some of these into a smaller number of listings (you can do this by editing one listing to include more files, and marking others to be deleted). This helps the readability of the archives, and it makes it easier for devs to keep track of your files as well if they want to use them.
It looks like you've incorporated some photo resources here. Is there any way you could reference those as well? It's important that these kinds of sources be tracked to make sure that they're properly licensed.