I have been in banking 5yr, a licensed banker 1yr. I do not process mortgages nor do I decision loan apps but I do know a little about this. 15% of your score is account history and part of that history is length of time for an "open trade". in other words - do not close accounts (credit cards) with a zero balance. The long trade history is a good thing.
now on the flip side - I know if you apply for a mortgage and you have to much credit available to you we the bank) may come back and ask you to close some of those accounts BUT the loan officer will let you know at that time.