My first thought when reading this was that, yes, you can mix Shimano and Campy drive-train components but only if you're using friction shifting. I was using mixed components on my vintage bike for a while until I changed everything over to Shimano except for the Campy friction shifters. I like having the advantages of hyperglide but don't feel any burning desire to have index shifting. But that's me.

Reading further into this thread, I see that the bike in question is much more modern that certainly uses index shifting. My second thought was that maybe the OP meant that the index shifting is working just as well as it was before. That's not the same thing as saying that everything is working perfectly.

Maybe something was out of alignment or needed fine-tuning, which was why the OP felt the urge to upgrade? In what way, I can't say because I'm not that intimately familiar with the nuances of index shifting.