About the same as they are without Horford.
You ever see Horford attracting premier free agents to Atlanta? I think not.
I don't believe Horford has nearly enough star power to attract big free agents. I don't see him bringing any more than somebody like Paul Millsap, Kemba Walker, Serge Ibaka, etc.
Those are all guys are good players, but not the type of players who will draw in Free Agent superstars.
If you go after Horford, then I think you need to do it based purely on what he adds to the team in terms of wins. I think the impact on free agency would be really quite minimal. Not saying it wouldn't help at all (Thomas and Horford is more appealing than just Thomas) but I doubt it would influence people much.