We once allowed a large Viburnum Tinus to grow old and large and it became bare at the base. Maybe it is an age related matter. A lot of shrubs do not remain entirely presentable over many years. No matter how hard you try to cossett them. Bit like us humans really!!!! Might be time for a fresh start but daunting if it is a hedge.

I had one of these, about the same age, and got a tree surgeon in to reduce it.
He removed the upper 40% and although it looked a bit sorry for itself initially it soon sprouted new growth lower down and returned to its beautiful former self.

It will rejuvenate if you cut it hard back .... that would restore the low down growth.
For the pest .... spray with a general insecticide and it'll probably be fine, i use a product called 'Bug Spray' on my shrubs, because they're always being eaten, .... it's in a red handheld trigger-spray container.