So, in short before I start rambling, is I think you should get one. They're relatively cheap, easy to use, and easy to maintain.

With that said, does your company pay for the re-certifications for the high-angle rescue? If so, they should cover the rest of the first aid training. If you are in the "wilderness", I would highly recommend taking a "Wilderness" class equal to your current certified level. They have Wilderness First Aid, Advanced Wilderness First Aid, Wilderness First Responder, Wilderness EMT, and Wilderness Paramedic. I think this will be more beneficial, as it transfers some of the liability to the corporation for equipment maintenance, and you don't have to pay directly for the classes.

Like Polak187 said, these individuals require advanced medical care for any problem the AED can help "solve". CPR is a labor intensive act, and you also need to keep in mind that you could be doing CPR for 20 minutes or more. Yeah, adrenalin will help, but there will be a point you and others cannot continue. It is kind of a given that any cardiac emergency in the wilderness or in a large natural disaster area will be fatal.

You should talk to a lawyer to fully asses your liability, especially if you become an EMT. There will be a different level of care there.

With some of the numbers you see for success rates of CPR and AED, people that have severe medical problems (i.e. heart disease, etc.) the tool is more of a way to help individuals feel that they tried to help. Not knocking it, I wish I had more time to train more people in emergency response, but sadly, that's what it seems to me to be a lot of the time.