Both 那里 and 那儿 are completely interchangable
Living in Beijing I should disagree just because, but you're right. ;)
Totally agreed (I'm a native speaker). You can also say 去那了？
So glasses and eyes are pronounced the same? (Although written differently).
No, they are pronounced differently also. Look at the tone above the 'i' in "jing."
Eyes = Yǎn jīng
Glasses = Yǎn jìng