I'm okay with paying him too, just not to a deal that will handcuff our ability to stay competitive. You just can't give into the whole "Rice deserves it" thing. This is a business, and it's just not wise to promise him lots of money for the future based on things he's already accomplished. RB's just have too short a shelf life.
It's good business to pay him though. He provides so much for the offense, it won't handcuff the Ravens. Reed will be paid less next season than he is this season which frees up room and i expect some players to not return. Trust me, paying him is not going to handcuff this team. I don't expect most of the veterans to be gone after this season though. I believe they'll be back as long as they can perform. No major contracts run out next season besides Flacco and Rice but I expect them to be done this season. I really am not worried about it.
You're assuming that he stays at or above his current level. If he does (and the more I think about it the less worried I am about it), it would absolutely be a good deal.
However, you still have to take into account the likelihood--for an NFL running back, very, very high--of injury or decline, often very fast. If he remains at this level, the offense will run through him and he will perform. If he doesn't for whichever reason, either the offense runs through a less-effective player or he isn't involved in the offense at all. Either case is bad news, at least as bad as him leaving outright because of the expense, and has to be considered by both sides.