In grammar【是】has totally changed the structure of this sentence. 【是】become the verb of the sentence. 我看你最好(是)去学生餐厅吃 What I think you should better to do IS to go to the dining-hall to eat. it is obviously an emphasis. but as this structure is so popularly used, It's not so emphasized，so that you think [好像没有太大的实际意思].

据你的理解，最后一句话里面的"是"字，的确没有太大的实际意思，完全可以去掉。“是”强调的是you'd better“去餐厅吃”，instead of"在宿舍吃"。 “要是” eg:要是明天下雨，我就不去旅游。“要是” means "if" “总是” 你总是在帮助我。“总是” means "always" “要不是” means "if not" “最好是” 你最好是去图书馆找资料。“最好是” means "you'd better"

谢谢大家，我又学到点东西了！顺便问一下，你们说这个“是”字也有相同的意思吗："记者：费先生，你是一个会计，你的工资应该说(是)相当高了，你可以过很舒适的生活。那么，工作对你意味着什么？"

one addition to my answer: when we say '最好' to warn sb. , 是 normally does appear. eg: 你最好乖乖呆在那儿,别耍花招!; 你最好抓紧来,否则很容易摔倒的!

I think it's the abbreviation of pattern "(最好)还是....(吧)" or "最好(是)...(吧)", which may show a meaning of offering advice, like 'had better' in English. It's a relatively fixed pattern i think and it's hard to tell what it exactly means here. To some degree, there are some slight differences between the examples below, but it's not easy to sense the differences so whichever you respond with, it makes almost no difference. 我看你最好去学生餐厅吃. 我看你最好是去学生餐厅吃. 我看你还是去学生餐厅吃吧.(adding '吧' appears to make the sentence sound more natural.) 我看你最好还是去学生餐厅吃. (actually I think "最好" gives more feeling of warning than "还是" does.) BTW, splitting hairs is not a bad thing : )