Do be aware that you can't sit for the CCRN exam unless you've worked full-time ICU for the last two years (the AACN's Website states "Practice as an RN or APRN is required for 1,750 hours in direct bedside care of acutely or critically ill patients during the previous two years, with 875 of those hours accrued in the most recent year preceding application"). Your manager must provide a letter of verification to that fact when you apply. Also, if you work overseas, your hospital must be either Magnet or Joint Commission International-accredited to qualify. CEN, on the other hand, doesn't have any "hard" limits on experience before registering, but they recommend at least two years experience in emergency nursing before attempting the exam.
Speaking for the CEN exam, ACLS and PALS were a minor help, but TNCC and ENPC were very helpful to have beforehand. I do think that having the certification has made me a better practitioner; in addition to the content benefit linearthinker mentioned, the CE requirements for maintaining the cert force you to be more evidence-driven in your practice. As far as tangible benefits go, I got a pin and my name published in the hospital's nursing newsletter.
Hope this helps!