Is there risk in getting a larger pressure tank for my well pump?
A larger tank will cause the cycles to be longer (slower), but overall the runtime will be  the same (if you use 500 gallons of water, the pump has to supply 500 gallons of water). For example, if the tank is full and you open a tap, with a 36 gallon tank it may take 60 seconds before the pump starts, and then 30 seconds to run, and repeat. With a 55 gallon, it may take 90 seconds before the pump starts, and then it will run for ~50 seconds. In both cases, this is ~33% duty cycle (if you excuse my rounding errors for simplification), and so if you leave the tap open for 10 minutes you'll get a total of 198 seconds or 3.3 minutes of runtime.

The downsides to a larger tank are simply that it costs more and takes up more space.

The only real problem is if you have too small of a tank you'll cause the pump to cycle too quickly which wears it out faster.