Almost all of the time I would agree with the people who are against cutting down a tree, but I'm going to say that there are reasons why I would agree with your decision in this case.

I've spent several decades as a professional horticulturist and garden designer and I'm an avid environmentalist. I'm proud that over my career I've been responsible for planting hundred of trees. I also feel the sentimental attachment to specific trees that makes me want to preserve them, and I appreciate the fact that the tree has spent 40 years growing and giving to the earth.

After saying all that, I will point out that unfortunately, silver maples are basically weed trees. They are weak wooded, and highly likely to have branches break in storms. They should never be planted close to homes as they can easily cause property damage. They also have very greedy surface roots which prevent anything else from growing under them. Verticillium wilt is a major disease problem, and it can cause sudden death. They can grow to more than 100 feet tall. Another problem is that they love moisture and their roots often grow into water and sewer pipes. It's too bad that this tree got a start in your front yard rather than off in a wooded location where it could live happily without causing a problem to a homeowner.

If you intend to replace this tree with 3 others, please do some research and pick species with better qualities that are more suited to residential front yards. In the long run, you will have a better landscape, both from the ornamental perspective and from an environmental standpoint. Sadly, all trees aren't created equal and saving a tree just because it's a tree isn't always wise.