We have two giant sugar maples immediately to the west which shade nearly our entire house, and for that we love 'em. They also provided almost two gallons of maple syrup this year. They are not long for this world though. I'd like to replace them, and obviously can put in a few sugar maples close by to get them started. They grow a little slowly though... My question is, what do you think of planting some fast-growing shade at the same time, just north of the new maples?
Can you phase them out one at a time? Start planting a few sugar maples as soon as possible in an area near them. It appears as though your fast-growing shade trees are a temporary fix to something you'd like to be permanent. I would want to keep those trees as long as possible, only removing severely rotted or loose branches that may fall on adjacent structures; otherwise let them be, savor their diminishing shade and maple syrup, and plant the new generation if there aren't already some starts or shoots coming up around them.