Frank..que sepa yo .. in all my time in Spain..never heard this expressed such...
que yo sepa ..as far as I know
que se yo..what do I know
Agree, you're right. "que sepa yo, no" "as far as I know, no", is common especially in the States, but not used the way I have used it. "¿Qué sé yo?" would be better. I have a Spanish course, and some of the content is based in South/Latin America, and it isn't the first time I have picked up habits that are fine there but not in Spain. Keep it coming, I never tire of having my Spanish corrected.
Most forum users or foreigners do not need to write correct Spanish..in fact only about 20% of Spanish themselves do..learning this takes up too much time which could be spent on vocab.. and puts a lot off learning and makes learning the lingo a pain.
This, of course, is a personal choice. On any given subject/hobby etc,we will all have different ideas on how much we want to learn about it. Some will delve quite deep, others will merely scratch the surface. Having a huge long list of words and not being able to string them together is not a lot of use. I personally like to try and get my Spanish as correct as possible, not everyone will, but that's just my choice. I have shared courses with people that are fanatical about perfecting their Spanish, look in wordreference.com, there are thousands of people from all around the world looking to perfect their Spanish knowledge. So I'm not alone, but realise it's not for everyone. I would think your 20% figure of Spanish writing correct Spanish may be true of rural Andalucia, but certainly not true of many parts of Spain
After more than 30 years here..speaking mainly Spanish to Spanish no one has ever complained with my own wee mistakes..
Doesn't surprise me, I have found that unless you specifically ask them to correct you, they are normally too polite to do it. When we meet Spanish trying to speak English, we don't normally comment on their mistakes. We have good Spanish friends, and he never picks me up, even when I know I have just come out with something stupid, even despite me asking him to correct me. However, speaking with a Spanish friend on skype, the whole idea is to improve your chosen language, and he is always correcting me!
But that's why I'm there.
Should stick to how to best pick up UK TV, and other more relevant subjects like how to rehome dogs/horses et al 
