I could be brosciencing, I could be right, I could get slaughtered here by hardened veterans or true scientists, I don't care. Just my 2 cents:
Strength could be put as this:
the ability to
-perform a given movement
Strength as displayable in any movement that is, but let's focus lifting.
Muscle moves weight. Or to be more precise, the contractile elements of a muscle (is that myofibrilar hypertrophy?) move the weight in the end. Nutritients ,mainly protein and fats, are the "building blocks" of muscles. Their is a point where getting more nutritiens in wouldn't help because your body can't build more in given time. That's the gist of this far better formulated and more elaborate article right here: http://www.T-Nation.com/article/bodybuilding/the_truth_about_bulking.
In this part of the equation I would say that a leaner bulk would be fine, enough is enough. And you have to shed all the fat afterwards, if you don't plan on staying that fat.
The contractions are all about intermuscular coordination. Being able to turn your muscles on. This is where +90% lifting has it's most prominent place. I can't really see why a leaner bulk would make this less effective. Just be sure you have the carbs to work out this hard and the protein and fats to manage your recovery (also neurally).
The last part is about skill. Can you do the move as efficiently as possible. This is where intramuscular gets into play. Being able to turn on and off the right muscle at the right time. Why would a leaner bulk hinder this? As above, make sure you get enough nutritients.
So from a strength standpoint, I see no reason to bulk up more than strictly needed. You may get a little chubbier, but getting really fat doesn't do much good.
Well, something can be said for getting fatter. A bigger belly can help your squat, and getting fatter around your your chest and shoulders can help stability and some decrease some range for the bench.
Hope it helps a bit