Plumbing fixtures are designed for a maximum of 80-psi. A water heater is tested to 300-psi, and the safety valve opens at 150-psi, and it will without an expansion tank if you have a closed system. The hoses that feed your faucets, toilet, and washing machine and maybe refrigerator's icemaker don't expect more than 80-psi. The seals on your toilet may leak or wear out sooner if your pressure gets too high. You're more prone to having water hammer when shutting off the water when the pressure is higher (it causes it to flow faster in the pipes, so stopping it quickly is the issue just like hitting something in your car at a higher speed).
A constant high pressure may be less problematic than one that gets higher, then is released, as that can stretch things, then they MAY recover...depends on whether that stretch exceeds the elastic limit of the item. Ever taken a steel coat hanger and bent it? It doesn't break the first time you bend it, but bend it back and forth for awhile, and it does. Water will bend things when the pressure gets higher. If you have a closed system, the thing that bends is the bladder in the tank (usually, a synthetic rubber), and it will last MUCH longer than other things, and it significantly limits the pressure change with expansion. It's important to precharge and size the ET, if you have one, properly, or you'll be exceeding its limits and prematurely wear it out.
With the likelihood that the utility company will (if they haven't already) install a check valve on your supply, IMHO, adding an ET won't hurt, and may solve a lot of issues either now, or down the road. They're not expensive, or hard to install properly. My city began requiring an ET to pass an inspection way back in the 80's, as the recommendation to install check valves had come out from the feds. This is not a new situation, but some are slower to implement than others.
Note also that as more houses are built, it is not unusual for the utility to add booster pumps or new water towers to accommodate the increased demands. They're required to provide a minimum pressure, but the maximum isn't as restricting. IF you live on say the bottom of a hill, you're pressure will likely be higher than a neighbor higher up. Just static pressure changes from elevation differences amounts to about 0.43#/foot change. So, your pressure may have been below 80-psi when the houses were built, but now could be different. IT also will likely change overnight when the utility may be replenishing water in the water towers and the usage is lower.