I drew these from D1A-only games in 2006, when the kickoff was also from the 35 (but touchback was to the 20).

Kickoff distance:
30-34 yards: 0.0% (0/78)
35-39 yards: 0.0% (0/125)
40-44 yards: 0.5% (1/200)
45-49 yards: 0.0% (0/246)
50-54 yards: 0.8% (4/489)
55-59 yards: 0.8% (8/947)
60-64 yards: 0.9% (13/1485)
65 yards: 1.0% (10/1052) [excluding touchbacks]

If your sole concern is avoiding TDs, kicking short is better than kicking long. But like you, I think field position is the key statistic, and the length of the kick and the return have no intrinsic value separate from that.