Looking for something to freshen up your playing? Here is something that is sure to help. It's not about better articulation, better intonation, or better dynamics. Have you tried energizing the rhythms? When you insist on accurate rhythmic spirit, you will likely notice all the above will improve. Rhythmic character also makes your playing a lot more fun for your listeners. If they have to listen to you, they might as well enjoy themselves. If you aren't enthusiastic about your playing, they won't be either.
Take the first movement of the Halsey Stevens Sonata for example. Better than being satisfied by offering an impressive display of notes, you could seek to grab listeners' attention with snazzy, snappy rhythmic character. Even with all systems operating perfectly, your performance will only be average if your rhythm does not have some sparkle to it. You can deliver an accurate deadpan, low energy rendition, or you can command attention and win prizes. Improved rhythm always makes a better product. Whatever you notice in the music, fast or slow, reflect it with good rhythm.
The Kennan Sonata is another one that gives you a chance to capture the audience from the very first note. With no long extraneous intros to wait through, it's just breathe and blow up a storm, but keep it steady. Obeying all the speed change signs is tricky but worth your extra attention.
Another obvious opportunity for instant rhythmic involvement is the Tomasi Concerto. Immediately, you are thrown right into some flashy whimsical fanfares. It's like the uncorking of a wine bottle, or a sudden burst of firecrackers. How about the The Hindemith Sonata, famous for that steady unrelenting pulse. Establish the pace, breathe deeply, release the tongue and enjoy the ride.
Great rhythm should be automatic and contagious. The audience is there to catch it.