In my experience, after a full on cleaning, of either hot water, surface change, oven, whatever you use... I notice a weakened reaction as well. Now, this is not because I think cleaning is a bad idea, but because I am a believer in 'break in' period and 'track condition'. Personally I get a better reaction once my track gets worn back in VS after a fresh cleaning, and this even applies to out of box for me. The first 6-12 games for me, the ball isn't all full potential yet, but once I get my track worn in, the ball becomes a bit stronger and a lot more consistent/reliable.
As for the discussion about plasticizers... It's true that heat does bring them to the surface, but I have yet to read about them coming all the way OUT of the ball. Meaning, even though the heat brings them to the surface, they remain ON the surface, they don't fall off the ball, or magically disappear. As the ball dries, cools, and is used, the natural absorption of the balls coverstock, actually sucks the plasticizers from the surface, back into the coverstock. Now, I can't verify this, or prove it, but it seems the most logical to me, and also follows along with what I described in the first paragraph about 'break in period' or 'wearing in the track'. Maybe what's actually happening is the ball is simply absorbing the plasticizers back into the cover stock, and once it does, the reaction comes back?
Take it for what you will, This is a question more suited for chemists who have bowling ball coverstock focuses.