Hey bashing around a tamiya can be fun. Having fun is the most important part. But if you're actually racing in a tournament with good racers out there (even local), it won't look so good driving a tamiya in terms of racing. There's a reason why you see Associated, Xray, TLR, and Kyosho out winning championships . You see racers learn from other racers. And you won't find anyone doing real racing using a tamiya because there really isn't any racers doing it to model after. Plus you're going against people that have racing kits that are built for the modern track. That's not what Tamiya is about.
I've raced locally and regionally for years. Even when I was a kid, I was lapping tamiya frogs, foxes, and hornets with my Ultima. And I was being lapped by rc10's (I wasn't as good as the rc10 adults).
But try it out. Nothing wrong with seeing what happens. What Tamiya were you looking at racing? There are some local races that have a novice open class. That might be the race you want to get in.