Hi,Anthony.
Here's a few words of wisdom that might clarify some of the points.
The Pro's - First of all, your pals will think your car is cool if you Plus Size. The bigger the diameter, the cooler you are (at least some folks think so). The biggest benefit from Plus Sizing is the increased road handling. By increasing the wheel diameter (and maintaining the original overall diameter), the height of the tire side wall deceases. This has the effect of less tire sway or roll, and increases the stability or cornering ability of your ride. Other than appearance and peer envy that is about it as far as the Pro's go.
The Con's - The effect on suspension. By decreasing the side wall of the tire, you will increase the effect of road bumps, pot holes, expansion joints and all the other deformities of our roads and highways. Road noise will be increased also. A few things to beware of when choosing to Plus Size. The larger the diameter of the wheel, the more difficult it is to meet the load requirements for a safe and reliable wheel. Some manufacturers solve the problem by adding material to the wheel so it will pass the performance standards. By adding material, the weight of the wheel becomes heavier than the suspension the vehicle is designed to take and function properly. The tire and wheel are considered unsprung weight, and can cause excessive wear on the struts or shocks, bearings, spindles and brake systems.
Plus Sizing is not a bad thing when done properly - for example when upsizing, unless the rolling radius is maintained as for the original tire then the car's computer can get upset and the speedo can read incorrectly.
Just a few points.
Ken.