Spider x Spider pairings arent that uncommon, but many people dont advertise the pairing because it still starts arguments. From what Ive seen, there isnt an increase of slugs/dead eggs/failure to thrives even after years of debate. There have been people swearing its lethal, youll get trainwrecks, increased slugs, failure to thrives since 2009 but no one has ever backed up that claim. NERD bred spider x spider for years trying for a super, and didnt seem to hit anything visually different, but also didnt get any of the negative issues people are concerned with (its in one of their videos, Ill try and find it).
I really think spider is just dominant like pinstripe. Even though we know you can make healthy super pins and pinstripes are just as common as spiders, when was the last time you saw a super pin? It just takes too much time to prove out, most people are working on other projects and theres no way a buyer can know they are getting a super except by taking your work. You dont even see possible super pins that often. With all the stigma of the super spider, at this point I think that even if someone thought they had one they would be tempted not to advertize it. Who needs the argument?