I thought that somehow I already answered this. I will try to do it better.
You pay long term contracts to Aces. Stars. Elite players. There are a handful in each position. Papelbon is in that category in his position. We paid Lackey as he was an ace. He was solid but not even close to be an ace. You do not do that. Theo constantly did that, reason why he is gone (among others). He signed average/solid/good players and paid 'em as if they were aces. I believe, you already know the cases.
Large market/payrolls teams are and arguably will continue paying long term contracts to aces. Our case match with this. The KEY is to know how/whom/when to do this. Yes, it is not trivial, reason why GMs are usually well paid in order to plan and execute that.
You don't miss an opportunity like this since aces do not grow in trees or just because you shitted the bed in the recent past at the FA. You just do the opposite. You learn and execute signing aces when available or at least you explore/try/do your best to afford 'em.. In our case we didn't even do that (We didn't even presented a formal proposal)
Yes, still there is a risk, but aces minimize it. Papelbon is an ace. Rivera is making 15 MUSD. Pap will make 12.5 M. There is a +- 17%. IMO it is fair, considering their numbers/performance and mostly since Papelbon is in his prime and is young but mature/experienced and well projected and Rive is the best.
Hope that I had answered your question.
We have plenty discussed this matter in other threads. I encourage you to read them for more fully details. Don't take me wrong but I don't want to pass through this again.