My first house was known as site 5 when I bought it. It turned into no. 13. I loved that house. Never had a days trouble in the 5 years I lived there. Our first child was subsequently born on a 13th too.
When we sold the house we got slightly more than a house 4 doors up from us, and that house had a £5,000 landscaped back garden (according to the sales puff). The houses had the same aspect and were over looked to the front and rear.
In summation, you'll always sell if the price is right. In my experience having no. 13 on the door didn't cause me any hardship come sale time.