We got all of our dogs quite close together .. the largest gap was between Maggie and Daddy. In the early years I would say it is definitely easier to have them fairly close together. Now Maggie has no time for Daddy because he's just too full of energy. Only the two schnauzers will play with him, because I don't think Schnauzers ever stop bouncing off the walls!!!
However, I do sometimes wonder about the medical bills in a few years time!! Coco will be 8 tomorrow (the shih-tzu poodle mix) and then the next one down after that is 6 - after that they are all pretty much close in ages.