Again, I don’t think the issue comes from you, expecting something unrealistic, you’ve said : “I was expecting to see sharp pixels”
To some people, sharp pixels are a disadvantage and I get that some people could be disappointed by the OSSC, thinking it would make their games higher native resolution or something. But you seem to know what is the purpose of the OSSC and you’ve also stated that “480 looks blurrier than 960”, so that’s a bit odd.
Nintendo console historically had bad video outputs and the Wii isn’t an exception. There is some color bleeding around the blue and the red on Wii.
Check this video from MyLifeInGaming, they talk about NGC games on the Wii starting on the 18 minutes mark. Maybe you can get some relevant info out of this video. (and also give you an idea of what to expect for you)
So, it maybe a combination of : cheap cable + bad video quality out of the box (+ probably a lack of fine tuning) and the OSSC making these flaws worse. You should look into the sampling options using this as a starting point : http://junkerhq.net/xrgb/index.php?title=Optimal_timings
and watch at least one of FireBrandX’s videos on the subject : https://www.youtube.com/watch?v=EBStHr4XCTg
This should make these settings less scary if you’re not familiar with them already. And also check his website : http://www.firebrandx.com/osscprofiles.html
He posts his findings there, this guy (if you’ve never heard of him) is really well respected in this community and rightly so. I guess you could use his NGC settings for your Wii as a starting point.
Also, don’t hesitate to ask around in a few days, I’m not the most knowledgeable around here but it’s a bit of a special period with the holidays, there are usually more people around here. So, expect more info from others once the holidays are over, this forum is usually more helpful than I am ^-^