Joined: Aug 2008
Posts: 13,127
Likes: 2,154
From: Ann Arbor, MI
Bikes: 15 Kinesis Racelight 4S, 76 Motebecane Gran Jubilée, 17 Dedacciai Gladiatore2, 12 Breezer Venturi, 09 Dahon Mariner, 12 Mercier Nano, 95 DeKerf Team SL, 19 Tern Rally, 21 Breezer Doppler Cafe+, 19 T-Lab X3, 91 Serotta CII, 23 3T Strada
If you're out to exercise, it matters not if you pedal the downhills, but rather that you put in sufficient work to obtain fitness improvements.
You can go around soft pedaling all day, but if you never elevate your heart rate sufficiently, if you never stress your muscles, you'll not achieve gains or improvements. Similarly, 20 minutes of hard work during a 60 minute ride, can net tremendous gains if you're working to a plan.
So, my thought is that for the OP, at this point, as a clyde self-limiting to 30mph on downhills, there's little benefit to you to pedal those, because even if you do, that doesn't amount to much work. Put your efforts into lifting your speed on flats, and pushing your limits on climbs.