The only negative I have ever seen with crossovers comes when you are trying to diagnose issues from one bank to the other. A "X" shaped cross over could make locating an issue based on exhaust pulse more difficult. A regular crossover with two tees and a crossover pipe would be fine for diagnosing. But other than that I can not think of anything. Equalizing the exhaust is a great idea to maximize power between banks.
I hope this makes sense.