You can have too many books. I adore books, I spent more than a decade working for Books Etc, Borders and Waterstones. About 7 years of that was working part time one day a week purely so I got the staff discount (not for the pay) because I spend so much money on books it is a good investment.
However I have so many (and I have a lot) that I currently have one massive attic room full of books plus piles in the bedroom, living room lined with them, piles in the kitchen etc etc.
Cluttering the house up, they create a lot of dust, plus I have a little boy now and he is going the same way. My New Years resolution is that I will have a cull.
I have come to the conclusion that you should only keep favourites that you genuinely will read again - be selective about what you keep, quality of the books you have is better than quantity.
Have a cull of books you won't reread and that your children have grown out of. They will do a lot more good being resold for a charity so that people who can only afford second hand can make use of them - they will be reread and enjoyed again rather than sitting unloved and unread.
And also make use of a library rather than buying books - it helps support a valuable local resource, saves you money and means that you have less clutter.
I agree lots of books are good, but from my own experience I know that it can get to much, my own DH is also making the threats of divorce if I buy any more books. Or cats.