Here's some food for thought...
How much are you really going to improve if you don't use those 2.5lb plates? Let's say you are going for a PR on Deadlift. You have just matched your PR of 405lbs.
Now, using this logic, you look past the "piss-ant" weights and throw on another pair 45's so you can really boost up your PR. Obviously, you fail at the 495, so your telling yourself "Goddamnit, 3 months and no improvement, I should change my routine again."
On the flip side, you add that 2.5lb plate, make the lift, and all of the sudden your PR goes up to 410. You are feeling good about it, so you take the 2.5lb plates off and add 5's to each side. You make the lift again, which brings the PR up to 415. Wow, that's a +10lb PR, you're fucking cock-diesel!
I'm telling you guys, adding a 2.5 per side each session will add the fuck up over time. If you do squats 4 times a month and add 2/2.5lb plates each session, that's a total of +10lbs more than you were doing last month.
Think about it.