What does 是 mean in 因为比读书有趣味的事情实在是太多了?
Actually, I think 实在是 hangs together. Your 是 I would interpret as 'those are'.

1因为     2比          3读书     4有趣味的事情 5实在 6是          7太多了。
1because 2compared to 3read-books 4have-fun-things  5really     6those are  7very many 

You could rewrite this:

因为有很多事情实在是比读书有趣多了。or 因为有很多事情比读书有趣多了。

在我的心目中，
To my mind,
一个好的作家是长生不死的，
a good author is immortal,
他的肉体当然也和常人一样，
his body, of course, is the same as normal people's,
迟早要化为泥土，
sooner or later, it will become dust,
但他的精神却会因为他的作品的流传而永垂不朽。
but his spirit, because his works are circulated, will not be forgotten and will be immortal.
在今天这种人人都想致富的社会里，
In today's world full of people seeking only wealth,
说这样的话显然是不合时宜
saying such words is evidently unfashionable,
因为比读书有趣味的事情实在是太多了。
because compared to reading books there are many other things which are more fun.