Beneficial bacteria (nitrosomonas and nitrobacter) will grow in relation to the bio-load (assuming your have provided enough surface area for it to colonize). All else bing equal, no matter how much more biological media you add, you will not grow more beneficial bacteria. At a certain point, you are just adding surface area that won't be colonized by the bacteria.
In my opinion, once you have provided enough surface area to keep ammonia at zero, anything beyond that is just creating crevices for detritus to settle, which is bad for your water quality.
So yes, IMO there is such a thing as too much biological filtration, when instead of it being colonized with nitrosomonas and nitrobacter it is instead acting as hiding spots for crud to accumulate.
In regards to mechanical filtration, the degree to which you filter will be up to how much time you want to spend on maintenance. You could use 1 micron pads/socks that will filter out things as small as bacteria, but you will likely have to clean/change it out every few hours.
Erring on the side of overfiltration is best, but at a certain point you will be making yourself a slave to the maintenance required to keep the filter functioning optimally. Like others have stated, at a certain point flow also becomes a concern. The extra electricity consumed can also be considered a waste.
