That would almost certainly help you get faster than you are now. Doing shorter, 10km as an example, at a target speed - faster than your usual average, could also help.
Personally, I prefer to do short, hard intervals on the Wattbike, in typically 1 hr sessions, and then be able to ride tempo and enjoy myself more, when on the road.
Does this make me faster? Well, not as fast as I was 10 years ago, but almost certainly faster than I would be if I was just riding steadily all the time.
Racing is also likely to make you faster - the racing itself is good high effort stuff, and the regime of training. Depending on where you live, and if you have the patience to get the through the long accreditation processes ( I don't!) Vets SQT sessions on the track will also help with speed. However, if you look at the times of over 50s, over 60s etc on the track, which is a comparable environment, you can see how age affects speed.
In short, we can go faster in our 50s (than we would be without specific training), but it does mean changing how you ride, maybe riding less but harder. For some people I can understand how this would turn an enjoyable recreation into a wearing regime ( at least, that's how I feel on a nice day when I would enjoy a relaxed ride in the countryside, but instead do specific hard efforts in a gym on the Wattbike)