It is true about the headgaskets failing at around 160k with the 2.5's, there was two design changes on them. If the car hasn't been through the recall then I would say do it, is there any way for you to find out from the previous owner? I'm not going to say not to do it because your absolutely right about them being a problem down the road if they weren't changed to the multi-layer steel gaskets.
I try to be optimistic about dealerships, they would seem to be more honest than an Indy shop but the nature of the business is to upsell...I have no idea how to tell that the headgaskets have been done before as I have never run into that with my own vehicle, if the motor has been pulled before you might catch a glimpse of a steel plate behind the flywheel, what that would tell you is that maybe the clutch has been replaced and the redesigned separator plate has been installed in place of the plastic one that came on the motor when it was new. If the metal plate is there, there may be a chance the headgaskets were replaced as well.
I know you have some decisions to make but if you are able to swing the cost of it then I would do it just as a safety buffer for your wallet and motor down the road. That's where peace of mind comes into play again.