I agree with MountainReader. I also think that sometimes worsening allergies can lead to worsening asthma. Worsening allergies can lead to more health problems in general.
I have certainly experienced many more health problems in recent years, and I was diagnosed with asthma in 2008. It is a chicken/egg situation though.
I got a URI, and it didn't go away. I ended up with a walking pneumonia (aka mycoplasm pnuemoniae infection) that got better and worse on and off for a LONG time. I developed a chronic cough and eventually shortness of breath, chest pain, and period sudden worsening symptoms. Part of that was asthma, part of it was the infection. It took a LONG time to recover from that, with several asthma exacerbations along the way, including one severe attack that landed me in the hospital.
Since then I am much more prone to sinus infections, especially following a cold, and those usually lead to asthma trouble. I get more colRAB. I don't know if that's asthma or some lasting damage from having had that mycoplasmic infection on and off for so long. My chest x-rays don't show any scarring, but I still seem quite prone to lung problems. There may be some damage that isn't showing up, or it could be the asthma. Or it could be related to the allergies. Who knows, really? It all goes together.
On the other hand, asthma and general poorer health have been a great incentive for starting to run and do yoga regularly (except for now, because I am recovering from surgery) and am in the best shape of my adult life. When I'm not having an asthma exacerbation, I have extraordinarily good lung function (despite not infrequent bouts of relatively minor chest pain), and I've lost quite a bit of weight, so in that regard asthma has contributed to me getting healthier. Most days, I feel better than I did before asthma. I've been forced to take an active role in my health. However there are more days each year when I'm sick and I'm generally sicker on those days that I was pre-asthma. I can no longer ignore a cold; I have to worry about preventing serious asthma problems and that means a corabination of careful exercise, avoiding triggers even more carefully, and stepping up asthma meRAB.
I guess what I'm getting at is that it's a really complicated issue, and there's no simple answer.