If you love them, then it was not a wrong decision. I bought a pair four or five years ago, I recently upgraded to Dekoni ear pad, which improved comfort by a large degree for me. i have since bought "better" headphones, but the M50x still come out for a week or so, once in a while.
As I upgraded my dac/amp setups, I found the sound on M50x kept improving.
I don't think you'll need to upgrade for a good while. Just keep listening to the M50x, until you notice something you don't like. At some point, you'll decide you need a pair of headphone that can handle what the M50x can not. This will helps to guide the next "upgrade" purchase.
In the mean time, Just keep throwing some coin into the future upgrade kitty as long as you can.