More than you might think.
For starters, now we don't have to draft Davone Bess, Legadu Naanee, and Brian Hartline in hopes of finding a mediocre starting wide receiver for the Dolphins. Every team must have a number one receiver. That doesn't mean they are always valuable in fantasy, but I can really only think of two teams (the Jaguars and the Browns) who had no receivers worth starting on a fantasy team. Now that Mr. Chad Ochocinco is in town, one of these players gains value. My guess is that Davone Bess will be the second best wide receiver on this team, and he should be better than he would have been if the other team's top corner was following him around all day. Anthony Fasano also takes a step forward, since he could have been the best receiving threat on this team before they signed Ochocinco. I still don't think Fasano has what it takes to be drafted as a legitimate fantasy tight end, but he is definitely in a better position.
The most obvious advantage for fantasy owners is that Ochocinco went somewhere without a great second receiver. Sure, those other guys are serviceable, but Ochocinco still has plenty in the tank (and I don't just mean game-livening antics). He probably won't be drafted until the 7th or 8th round, but he'll probably hold some value. Think of him as similar to what Reggie Wayne will do this season. Odds are that Ochocinco will catch fewer balls with a higher yard-per-catch rating, and I would say that 1,000 yards and 5 touchdowns is a pretty reasonable estimate. Ochocinco's best bud, T.O., was able to muster 983 yards and 9 touchdowns in his last season with the Bengals. He was older than Chad is now, and we all know that Ochocinco is in shape. Even if his route running is a bit lax at times, at least he will be able to get some separation and win fights for the ball.
Reggie Bush is the last guy who will benefit. Can you imagine how keyed on the run opposing defenses would have been? They probably would have played 2 corners and a safety against a 4 wide receiver threat. Now they have to respect that fact that the Dolphins have a receiver who can exploit man-to-man coverage. Bush is going to sleep much better tonight because of this signing.
The Dolphins get better with Ochocinco, like it or not.