Hi Gayle,
Certainly memorising your music will improve your performance of it in the long run as it frees up mental capacity to allow you to focus on the tone and feel of the piece. Lets take this top level professional concert as an example.
The orchestra members are using the music- the conductor is doing a lot of the 'feel' and enterpretation 'work' for them. The conductor and soloist themselves know the piece intimately and work without the sheetmusic, and this frees up their capacity to put real feeling into the performance.
Basically, reading the music is taking up brain space in the moment that you could be using for listening and adapting. It takes a lot of work to memorise a piece of music but as you have found it can allow you to improve your performance.
Robin