I don't see any real functional difference between Roberts, Holmes, or the forgotten Streater. Each brings something to the table- Roberts can block, Holmes can jump, and until he went into witness protection Streater could catch. None are that special, but again as third options they're fine, and there's no glaring need to upgrade that position group.
The key to improving the passing corp generally is already on the roster in the form of Walford. He turns into a 50-60 catch safety valve and red zone mismatch, I could give two shits how these three do next year, or who the third WR is. He's where the most improvement can come from in terms of pass catchers.