Although I don't have the Xpression, I do have both the Replifex and Intellifex units in my rack (with Triaxis and 20/20). The Xpression has nearly identical effects options as the Replifex, but Xpression has special features for bass, as well as a higher 24-bit sample rate - an improved Replifex.
It's true that the Xpression has more variety of effects than the Intellifex. You can get phaser, tremolo, flanger, and rotary effects not in the Intellifex. This is also true of the Replifex, and years ago, when it came out, I thought it would replace the Intellifex for me. But I found that I preferred the reverbs (more types, better sounding) and delays (especially the delay ducking feature) of the Intellifex. I kept them both, because each is unique. After many (nearly 10?) years of faithful service, I'm still happy with both.
If you're considering changing out to the Xpression, I recommend comparing the delays and especially the reverbs on the two units before deciding.