Some thoughts. This isn't a criticism of DC, the Flash, or his fans. Rather, it's an attempt to place his powers in perspective.
I don't buy the Infinite Mass Punch. If Wally really were subject to relativistic mass dilation, his body would tear inself apart long before he ever reached lightspeed. Furthermore if he were subject to relativistic affects, were he to attempt a speedblitz at greater than 90% lightspeed Wally would be the one who couldn't react fast enough. At .9c 2.3 seconds pass for the body at "rest" for every one second for the Flash. At .9999c 70.1 seconds pass to the oberver at rest for every one second that passes in the Flash's frame of reference. This would introduce all kinds of problems, not the least of which is getting-smashed-by/left-behind-by the planet Earth as it moves through its orbital curve.
The Speed Force is essentially magic. It lets him move outside the rules of spacetime physiscs, but according to some other (poorly defined) rules of its own. While it pays some lip-service to Relativity, it shields DC speedsters from any of it's actual effects. Furthurmore, it protects them from things like the impact on their joints, heat from friction, flying off the planet when they exceed escape velocity, having their faces rubbed off by their bow-wave while their GI tracks are sucked out their rear by their backdraft, and so on.
When he punches someone at superspeed, he's not hitting with the momentum of a human body at high velocity. It's essentially a speedforce force-bolt coincident with his hand. When he runs, he's certainly not propelling himself by pushing against the ground.