You are one of the crazy rare dissenters that doesn't pair the C3 with the BH, correct? If so and you are using the C3 solo, then yeah, the X3 might be worth the price of admission. The C3 alone sound great, but the extra power that the amp provides can really bring out the best in a lot of gear.
Nah, I've already stated why I don't pair the two - first, synergy with my inventory (the only ones I like with that combo are the vsonics and s500 and use neither of these on the go) and second, the lack of proper bass boost coz while the BH has a bit better clarity and bigger soundstage, its bass "boost" is pretty bad IMO (and not only because it boost the top end) and doesn't do what the C3 needs, which is to add sub-bass and better control as the C3 has a bit of bass roll-off. The E11 handles that better even though it's slightly behind in overall power.