Probably the best way to improve your times is either to train a bit harder or run a bit faster on the day! However you came to this post because of the title so here goes on ways to get a better shoe.
1. You will get a lighter racing shoe by buying a “Running Flat”. These are race day shoes that are probably about 500g or so lighter than the shoes you already have. By my calculations that weight loss will save you a couple of seconds at best.
2. Sorbothane insoles for your shoes will reduce impact. I don’ t think in themselves they will make you run faster but they might make you less injury prone and hence increase the time available to training. (They worked for me). However I would have to say that decently fitted running shoes these days have all the cushioning and support that most people need.
3. Elastic laces mean you can get your shoe on and off faster. That could decrease the 5k time in your duathlon or triathlon. Although technically it is your transition time that is reduced.
So I think running is just one of those sports/activities where (beyond a good pair of shoes) extra kit doesn’t in itself make you go faster…it just help you get faster by training better. Sorry!