Most people would be better served losing a couple of pounds of bodyweight...
I have to disagree.
Although losing weight will serve you getting fitter and enjoying your ride more...
Which is quite significant, no?
it wont make your bike feel lighter & whippier, it wont get you up & over obstacles easier (within reason) , & it wont accelerate any more rapidy.
It won't make your bike feel lighter - but that won't matter quite as much - you'll likely be fitter, and lighter - and as for the rest - yes it will help.
Your combined weight will be less - so you'll definitely accelerate quicker - especially if you are fitter. And there will be less mass to defeat gravity to get over obstacles.
Lighter bikes, especially in the frame & wheelset area, feel faster/better/more nimble than a heavier equivalent no matter what your BMI is.
I'm not denying that light bikes have a feel of their own - but the laws of physics simply can't be defeated in the way you imply.
By all means lose the weight though, it improves the overall package!
Which is just as significant.