Simon, simpler geometry probably does reduce render times, especially if you have reflective surfaces.
Simpler geometry generally takes less time to draw, is easier to edit and causes reduced potential for stalling the computer while you are working.
When drawing the detail stuff, consider the return on your investment. For example with drawer pulls, when viewed as part of an entire project, does it add anything to that project if you draw it in a highly detailed fashion. Is it worth your time to draw a hinge with both leaves and the pin as separate components? Do you even need the pin? If the model is a hinge, maybe. If it is an armoire or a cupboard, probably not.
Use that sort of thinking before you go crazy over modeling your model.
This reminds me of my days in school when I worked on musicals and stage plays. We didn't use real bricks to make a brick wall for a set. sawdust mixed with a bit of reddish brown paint and glue on canvas stretched over a wooden frame worked just fine. From the point of view of the audience, you couldn't tell they weren't real bricks and from the point of view of the stage hands, they were easier to make and move around.