I'm a big believer in preventative maintenance and preventing potential known problems where they are known to exist. Whether that is a right fit for you or not is up to you.
As an example, while not Ranger related, is a similar situation. The Honda 2.0 liter family of engines has a known issue with exhaust valves tightening over time and burning. Depending on the make of the vehicle, the recommended adjustment period varies but the solution remains the same. The Acura owners manual mentions the adjustment interval but the Honda one does not and only mentions that the valves get adjusted if noisy. That is very misleading since a properly adjusted valve train sounds like a sewing machine and the tighter the valve train gets, the quieter it gets. Many people have driven with this engine for a long time and never adjusted the valves and never had a problem. But when the problem occurs, it is at minimum, a $3,000 repair bill.
Looking at the timing chain issue on the SOHC and what is all potentially involved in a repair if things start to go wrong and if you don't have the ability to do the repair yourself, the repair could end up being a pretty high one as well. Would be $3,000? Probably not. It's more of a labor thing than a parts cost thing but there is a lot of work involved in the repair.
So, with all that being said, is $80 plus your time and some coolant replacement every 70,000 miles worth your time or would you rather just run with it? It's not a required or even listed maintenance item in the owner's manual. So, technically, you aren't wrong if you don't do it since Ford never mentioned anything about it. It comes down to you and what you feel you should do.