I completely agree - don't try to put your foot down while still on the saddle. Also, when you put your foot down, put your heel down on the ground first. If the heel area on your shoe is slippery, you could add some thing grippy there - tape or something. Both my sets of road shoes have little rubbery bits on the heel that are less slippery than the cleat.
Keep with it, those are easy-to-use pedals.
To muddy the water, however, my knee doc told me not to use the speedplays, b/c there is too much float and it makes your muscles have to work to keep the knee aligned - a pair of less-floaty pedals, positioned perfectly, is better. They told me to use Look Keos with the red cleat.