The TC3 is a great bit of kit, and you should be able to pick 2nd hand ones up very easy now. I know, you already have one, but whole cars come in handy for spares at cheap rates
You can drive a TC3 at a competative level but you have to really hussel the car, The drive train is a weak spot. Its just not efficent enough. Depending on the level of competition will depend on if the TC3 is right for you. In many places you can put a TC3 in the A. However at locations were the quality of racing is very high you'll find you need to have the best everything in your car to keep up. You'll be forced to really focus on every aspect of the car and keep everything perfect on it to keep up with the newer cars.
If your getting back into RC the tc3 will be great for you. If you find yourself at a dead spot where week in week out your constantly 1 or 2 laps down on the top guys, no matter how hard you push with no errors in your perforamnce then dont go throwing money at the car. At this point, its time to move on.