RE: Reseeding a clover plot?
Sounds to me, that you may have a better stand then what you think. If the bare ground is only a few inches, you are find. If it is over a foot or so and/or is bare in many areas over a few inches, you may do some good by overseeding. No stand of any type of vegetaion will have 100% (or even 90%) coverage of the ground. In winter and early spring, stands may look worse then what they actual are due to the height of the plants and that they don't cover all the bare ground.
What the others are saying is that the seed will have a better germination rate on ground that is bare and even a greater germination rate on ground that has loose dirt on top. However, if you damage the existing stand, you may not help yourself out much. There is some point of your plot's life when the plant density is low enough to where you can lightly tilled the ground to get better germination rate and still do minimum harm to your existing stand.
Anyway you go, broadcasting some seed will likely not hurt much outside of spending your money. If the clover is thick enough, the older plants will out compete the new seedlings that do grow (Weeds will do the same.). If the clover is on the thin side, some of the seedlings will survive and help fill in the plot.
Good luck.