I ask this question because I am in process of building my rig. If its a stupid question, please forgive me. I slightly know the obvious difference, but would there be any reason to invest in both (on a budget), or just go with a dolly/track? I just recently bought the CobraCrane 1 and am just looking for some tools to enhance my production value so I dont have to make up for it in post-production. Thanks in advance.
If I'm reading your post correctly you're talking about the difference between a slider that can track a subject for about a yard (.9144 meters) versus a dolly which is either limited by how much track you lay, say 10 feet (3+ meters) or more, or, if you have a lot of track or are on wheels on the floor, a lot more. It all kind of depends on what you're shooting. Is your subject a foot tall object (slider) or the length of a room / one or more people (dolly)?
Personally I like flexible tracks, in my case the "Spider Dolly" because it can go in a straight line or be curved to do a 270 degree or more swing around a subject. But then I'm usually shooting bigger things.
To get back to your question, though, both add production value and both require a level of practice to obtain smooth results. If you get skilled with the Cobra Crane you may find that you have enough control of movement that you don't need either.