Neal, when I first started buying DA roses I followed the recommendation to buy them in threes and plant them 18" apart (they do recommend planting different varieties further apart). It does make for a lovely big display very quickly, BUT I discovered later that planting a single plant can give wonderful results - I have planted a single Lady of Shalott in France, which after three years looks amazing, and very nearly as big as the group of three Lady of Shalott that I have in England. Since then I've been planting in singles (and saving quite a bit of money in the process!)
The exception is my Harlow Carr hedge, which of course needed lots of roses planted close together (3 rows of them, 18" apart).
So my sense now is that your instinct isn't far off right!
