I heard people bashing with their buggies and race with them say that they develop a lot of slop from bashing, and that they wish they did't bash with it. Where is the slop? I am going to bash my buggy for now but what If I want to race later. Will I need a whole new buggy?

No you wont need a new buggy. But I think the slop they refer to is in the steering as the linkage is designed with a certain amount of 'Backlash' inheirent to it. Otherwise it slows the steering as it gets dirty.

So when I want to race I can just buy a new linkage.

Slop comes from hinge pins, knuckles, ball joints and anything else that develops wear over time. If you can take your buggy, and move the front wheels in any direction, side to side, up, down, in, out, anything.... that is slop. It just makes reactive driving more difficult. If your suspension was always sloppy, you would be in a world of hurt in a racing situation if it suddenly tightened up, that is just being used to the way your car works, and being able to adjust to its characteristics. But since most people start with a tight car after mods, etc. loosening it up tends to change the way it drives. Since bashing puts extra wear on parts and changes the way it reacts, most folks who like to bash have a bash buggy, and leave the real thing for race day. That way, at least one thing is consistent on race day when it comes time to figure out what springs, shock oil, etc. is going to get you around the track the fastest.