An aftermarket clutch will grab harder, engage faster and can hold more horsepower than stock.
An aluminum flywheel (if that's what you mean by "new") will decrease rotating mass, freeing up some power that would normally be lost to the drivetrain. It can also offset power losses to larger wheels or bigger brakes.
Both are definitely worth it in the long run, however, I wouldn't suggest them as first mods. I'd at least wait until your stock clutch is starting to show signs of dying, or if you have the transmission off for other work (LSD, drive gears, etc.) Dropping a transmission is expensive if you pay to have it done, and its a nasty job if you do it yourself.