[Cyberdemon]

Generally yes they are purely cosmetic - I don't think anyone would be able to seriously quantify the handling benefits of an additional ~1" of overall track width on handling.

The handling and tire wear changes are also minimal - it is similar in effect to buying an aftermarket wheel with a different offset. Compared to suspension modifications which change the geometry and handling characteristics more dramatically.

As far a failures - it could cause your wheel bearings to fail earlier than normal, but again it's no different than if you got a set of aftermarket wheels with a different offset. As long as your wheels are properly torqued and the spacers are hub centric so they properly distribute the load I would no be worried unless you're planning on keeping the car for 200k miles.