They're still bad because they give worse field position, but they should reduce the big play (probably because the ball is closer to the cover team when caught). I looked at this using 2006 D1A games (also kicking from the 35), and these were the percentage returned for a TD, excluding touchbacks, by distance:

<30 0.5% (on-side kicks, 1 TD in 197 attempts)
30-34 0.0% (0/78)
35-39 0.0% (0/125)
40-44 0.5% (1/200)
45-49 0.0% (0/246)
50-54 0.8% (4/489)
55-59 0.8% (8/947)
60-64 0.9% (13/1485)
65 1.0% (10/1052)