Seeding SecureRandom from user touch events in Android

I'm creating Android app that will generate securely random 256 bit keys. I would also like the user to have the option of generating random bytes from tapping / dragging on the screen that will seed the random number generator (kind of like how TrueCrypt generates its keys). It looks like SecureRandom is my best bet, but I'm having trouble understanding the setSeed(byte[]) method.

Here is the documentation:

Reseeds this random object. The given seed supplements, rather than replaces, the existing seed. Thus, repeated calls are guaranteed never to reduce randomness.

I'm planning on taking the X and Y coordinates of the user's touch events and hashing them, then feeding the bytes from the hash repeatedly into setSeed.

My question is, will subsequent calls to setSeed strengthen the existing "randomness" or will it be more or less useless? Or is there a better way to achieve this that I'm completely missing?