Hi DassYochid.
I am no expert, and I may be wrong, but I would think the concentration may be more on remembering the words than concentrating on the feeling and thoughts behind them. How can one really do all three successfully (remembering correct words, corresponding thoughts, and increasing intensity of feeling)?
It seems in all cases, and I may be wrong, of making brachos, I have always read it is better to read them even if one knows them inside and out. I have never read where it is preferable to eventually recite by memory.
Is it a merit to strive to daven without a siddur?