My thoughts on the stock bridge are that it is awesome in design, but fairly poor in execution these days (especially in the standard, and MIJ stuff). 2 primary reasons for that.
1 - It is of minimal mass (aka cheaply made, as cheap as possible)
2 - It couples to the body very poorly. The fender entry level bridges (maybe all) are stamped out of a press. What is the retooling schedule like for that/those presses? A stamp press, like any other machine requires maint. The working surfaces of those stamp presses take CONSTANT wear and tear and over time perform less than optimumly. This creates a situation where the underside of each of those bridges is less than truely level/flat and causes it's surface area to contact the body at less than 100%. This, in my opinion, will affect sustain and tone negatively to variable degrees.
But, all of this in my opinion personall experience and potentially unfounded in your respective scenarios? Although, if you test one of these bridges by applying a micro-thin coating of say charcoal (pencil, not briquet) to the underside and then sit it on a piece of paper, what % of the underside leaves behind a trace of the charcoal? I have seen this done with two different stock Fender bridges and both were at 75-80%.
On the other hand, the probable impact to tone of all this is likely imperceivable to the average ear, so who cares?
Truth be told, I switch my bridges because I like to mod things (basses, cars, computers, etc)...
