Aside from voltage drop, a loose connection usually causes undesirable heating and consequent damage, so a onceover of inside-the-building splices and terminations is probably in order. It will also give you a “bargaining chip” to deal with the utility.
There are usually two parts of a circuit with different “owners”… and both can contribute to lamp dimming during heavier loading. Remember that the obligation for voltage support by the utility effectively ends “at the meter.” Motor starting is often a tricky issue, and there can be seasonal conditions that may have to be tolerated.
