This is a hard question to answer because the benefit of vector control depends on many factors including 1) the sources of virus inocula, 2) the size and activity of the vector population and 3) the type of virus.
Most airborne vectors of virus entering a dahlia planting will not be carrying dahlia viruses. Therefore the most likely and important source of virus is your dahlia collection. Did you plant infected dahlias? If so there will be a greater need for vector control.
The level of vector activity (numbers, types, amount of migration) varies from year to year. Temperature, rain, predator populations, length and severity of winter, daylight length, types and quantity of vegatation in the area and many other factors influence vector activity. Some years vector populations will be so large and active that protection of dahlias from virus will fail. For example, in the Palouse region of Eastern Washington 1 year out of about 7 the aphid population is so active in the spring that field peas can not be adequately protected from virus and serious loss results. It is not possible to predict that 1 year ahead of time. Most other years aphid populations can be controled and plants protected from virus.
Airborne viruses differ considerably in the rate of spread. Viruses such as CMV can rapidly spread short distances quickly. CMV is efficiently spread by many species of aphids but is nonpersistant in those aphids. In contrast, DMV is transmitted by fewer aphid species but aphids retain the virus longer and can move it farther. It is semipersistant. However, it is not certain that all strains of DMV are aphid transmittable (see section on DMV). Another example of differences are seen with the thrip transmitted viruses. Tobacco streak virus is transmitted less efficiently than tomato spotted wilt virus. Problems with tobacco streak are rare in part because large populations are needed to spread the virus.
The answer to the original question is that vector control is important and can help protect the dahlias from virus but it will fail at times and will have no effect on the incidence of some viruses. Because there are 2 stages to any epidemic (introduction of the pathogen and local spread). Eliminate virus sources, and control the virus.