I actually leave it in 1st most of the time, but I think that we usually have tighter and more technical courses than some of you folks.
The point the instructor was making in my video is pointing out how much time is lost to wheelspin. It's not like I wasn't being careful with the pedal either. It really did make it apparent how much I was losing even with moderate wheelspin...
I did eventually end up going faster in 1st gear, but I learned to be very careful, and it took driving around in 2nd gear most of the day to learn how to use and maintain momentum enough to stay quick while being VERY easy on the gas pedal. You learn a whole lot more about maintaining momentum when it's a lot harder to create it!
I would leave it in 2nd on the vast majority of courses, as it takes about .5 second to shift (time not spent accelerating), and most likely you will be shifting back just a few seconds later. Not to mention that it is unsettling to the car while cornering and opens up opportunity for rushed shifts that leave you sitting in neutral and screwing the whole run. I think you should only shift when it's a situation like Ilcowil's course, where you are coming fast into an extremely tight corner.
Don't waste another minute waiting on parts, or anything else. Just get out there and start racing! You will suck at first, and you will be slower than many other cars, but the only thing you will regret is not starting earlier...