Two rhubarb plants will take half that bed, which is not a lot of asparagus to start with. Another possibility is interplanting with self-seeding greens, such as corn salad, arugula, or miner's lettuce (effectively perennial). They would not bother the asp, grow well in partial shade and you would get two crops. The big con is that they would then be incompatible with mulch, which is always a good idea in the asparagus bed. So your price for the second crop is weeding cmp to no weeding.

It looks like a picture winged fly. I see them around, don't think they cause any trouble.

Yes, L. inflata will try to blend in but the foliage is a bit coarser than L. siphilitica and the flowers tiny as you confirmed.

Not sure of that but definitely a "foe" growing underneath - Lamium galeobdolon, aka yellow archangel. Invasive just about everywhere!