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The tree companies are correct that your birch tree is susceptible to the bronze birch borer. It looks like it has already lost several large limbs from the canopy. I'm not sure if they were removed because of decline or if you were trying to control the size or shape of the tree. If it was decline, you may already have birch borers attacking your tree. 

Given the location of your tree, I think it is only a matter of time before it is attacked by the bronze birch borer. The bronze birch borer is widespread across northern North America. Of course, I could be wrong, your tree could be the exception, but birch trees typically do not like growing in our suburban lawns. The growing conditions weaken them and make them more likely to be attacked by borers and then succumb to the damage. 

Here is a publication from the US Forest Service about bronze birch borer. It states "Adult bronze birch borers primarily attack birches that are weakened or stressed by drought, old age, insect defoliation, soil compaction, or a stem or root injury. Birch trees prefer cool, moist
growing locations and have a shallow root system that is easily injured by disturbance or dry, hot conditions. Many landscape birch trees are planted in unsuitable habitats and are stressed on a regular basis."

There is a section on management techniques (page 5) that should be helpful to you. The diagrams on page 3 of canopy decline might also help you make decisions. 

Here is a resource from Oregon State University that explains treatment and damage levels. I think it is important to note that once the tree is infested, it is harder for it to recover. There is a certain point at which the tree will not recover (once 40-50% of the canopy has died).

If you hire someone to treat the tree as a preventative, they will need to return and treat the tree every year. This is not a pest that is going away. Whether you treat or do not treat the tree is up to you. You may decide that it is not worth it, that you will let the tree go until it is clearly dying, and then replace it with a tree better suited to a suburban front yard. That might be years down the road and you are okay with it. Or you might decide to invest in the tree and try to make it live as long as possible. If you take that route, I would follow the recommendations in the US Forest Service publication above, and put a mulch ring around the tree, water it, etc. 

I hope this helps.