It depends....
My iMac is 11 months old. This week, I needed to decide to buy AppleCare or NOT. Since no screen issues, no disk issues, no "internal heat" concerns, I decided NO. If I pushed my iMac 8+ hours each day, know its internal runs hot, wasn't happy with internal hard drive sounds, etc, etc, then I'd say AppleCare is worth it. It's like buying extended warranty. If you drive a vehicle everyday, then its worth it. If you drive vehicle short distances only 4 days a week, then perhaps its not worth it.
Your call - based on usage and how your iMac is running now... And, one's individual risk tolerance level...
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