Well, I hate new Spreads, but I know quite a few now. I've created them over the years. Every once and awhile I 'try' a new Spread; it goes awful. The first few times with it are always awful. Of course, I normally have to either create or modify a Spread anyway, to fit my crazy head.
But the point is, using the same Spreads is natural... your cards do what they know and communicate with you how you've taught them. It's like playing a song you know perfectly, versus learning a new one. One is going to feel more natural to your hands, and the other is going to create a new perspective. Neither way is wrong or right, but understand the limitations of change, as well as the limitations of staying the same.
Of course, if the Celtic Cross works, why change it?
Or maybe you can change it a little at a time. You know, the Celtic Cross isn't really a Spread perse...it's a genre of Spread which can answer any question and no question at all. I mean, I change position meanings from time to time, and even without that, *your* Celtic Cross probably isn't *my* Celtic cross, etc.