i tried one out like this on my right space bar, similar method to what you did but i used flush cutters and clipped them, then used some vinyl to make it fit. it wasn't really that i didn't like it it is that i didn't notice a difference, just more sound.
I think you may need to give it more time.
For example.. words that have higher row letters or numbers near the end ;uio7890
These would require you to move your hand UP a little.. so when you hit the bar, it'll be near the upper edges..
Conversely if you have nmy,./ near the end of a word, then you'd be on the lower edge of the space key
These are the places where it makes the greatest difference..
If you test it by just tapping it in the center, yea, it won't make much of a difference..
Also.. lots of lube takes away the rattle noise..

That's the thing bout costar.. they rattle, but because of the loose contact, the action is much smoother than cherry.