First off, I am not a barrel racer. But my BO is, and I consider her a great horsewoman, so I will share what little I have learned from watching.
What ruins a barrel horse is having it run too many barrels.
What you want is a supple, athletic horse who is very sensitive to rider cues.
If you run barrels all day for 'practice', you might very well produce an excellent barrel horse who won't be much good for anything else. So, in other words, if all you do with your horse is gallop and spin, then thats all he will want and expect to do.
Condition your horse with a lot of long trotting, and run the pattern only occasionally, so that it is familiar yet fresh.