As to frequency and sustainment of Sims training:
SWAT trains with Sims at every long quarterly training session (2-4 days), and usually every month.
Every other officer in the department does "tactical qualification" every six months. It is part of firearms qualification and is mandatory for all officers. That is an 8-hour training day, usually at MOUT site at a nearby Army post, dedicated entirely to tactical training. The main focus is on the fundamentals of building clearance (by our doctrine, which was developed in-house and adapted from SWAT tactics), with additional empahsis on active shooters, mobile field force and specific scenarios, often to address specific situations that have come up on the streets since the last qualification cycle. We typically go through an average of 100 rounds per officer trained, per day, but most of that is shot by bad guys (especially if you are doing active shooter).
Past scenarios have dealt with suicide by cop (based on an incident I was involved in), officer hostage, high-risk stops and anything else we could think of. I have gone from being one of the troops to one of the trainers on this. The best part of this training is that it gets you past the "startle response" to high-risk situations and gets you thinks, acting, and using your tactics (not to mention your sights). The first time someone gets into a sims fight, they exhibit all of the "classic" gunfight symptoms: tunnel vision, fire the whole mag in on long inaccurate string, no sight usage, hits on the BG primarily to the weapon hand/arm, among others. After you have done it a few times, you start to remember your tactics and marksmanship skills. You also remember not to do bad stuff because it hurts to screw up. I am certain that this training has kept me out of shootings, and since I started doing this, some of the real life hairy stuff I have been to was easier than training. I recommend everyone in LE do this training and make it a priority that is performed regularly.
Oh, and if given the opportunity, do not be a bad guy for active shooter training. Longest week of my life.