Reducing weight helps in straight line speed but not as drastic as one would expect. You're certainly not going knock off a tenth of a second in a quarter mile for by losing 25-50 kilos which is quite a lot of effort if this is your daily car.
The difference you make in losing 25-50kilos would be more beneficial in the corners as compared to straight line.
The rule of thumb in losing weight is that you rid the non essentials first as they are cheaper. Eg. Rear seats, door trims (quickest, easiest) and the above of what you mentioned.
After that you really have to spend money to replace essentials with lighter parts. Eg, CFRP seats, A/C removal, lighter LSD, Diff support brackets, CF propshafts, Stereo, CF doors boot bonnet (if aluminium, there may not be much trade offs), rims, rotors, calipers, rollbars, exhaust, radiator, IC pipes. etc etc
Can't say for the other vehicles, but when I did the figures on my Evo 9, I was looking at about $250Aud/Kg saved. About $336sgd.
Not applicable in Singapore context. But if one is chasing weight, best buy a car that comes light from factory.