I just changed the pressure switch from a 30/50 version to a 40/60 type. Since then the water has a plastic/solvent type smell. What could cause this and should I be concerned?

Changing the pressure switch would not cause an odor in the water. Now that its too late, the 30/50 switch and the 40/60 switch are the same switch, just adjusted differently.

Unfortunately, what comes to mind if you are now getting an odor after changing the switch, is a ruptured bladder. Assuming a bladder tank, the correct precharge air pressure is relative to the cut on pressure of the switch. The precharge air pressure should be 2 pounds less than the cut on pressure of the switch. That way the pump comes on just before you run out of water in the tank.

If you did not adjust your precharge air pressure, the bladder may have expanded beyond its capability. Water is pumped into the bladder. The precharge air is between the bladder and the tank. If the bladder ruptured and water is coming in contact with coating of the interior tank surface, that is probably what is causing the odor.

Turn off breakers to pump. Depress the needle of the tank valve stem. Let all the air out. If after letting all the air out you get water, you have a ruptured bladder.
To recharge your tank, drain the tank and pressurize the tank to 2 lbs. less than the cut on pressure of the switch, in your case 38 lbs. If you do not have a drain valve at the tank, open the lowest faucet. Pressurize the tank until you have pushed all the water out of the tank. If you have a ruptured bladder you will get air out of the faucet. If the bladder is not ruptured you will not.

Then adjust precharge air pressure. You must use a tire gauge to measure precharge air pressure at the valve stem, not the pressure gauge on the tank.