RAM isn't expensive
You can get a 2x1GB module for £20 or so over here (about $35) of PC6400RAM without heatspread and that is at 4-4-4-12 latency (lower=better, not higher)
The stuff with heatsinks/spreaders are for overclocking, RAM is very sensitive to power and often if you have all slots filled on a mobo you will need to knock the voltages up a little and if you OC or UC often the voltage will need to be increased. This increase in voltage makes a huge difference to temperatures (as i said up there, memory is very sensitive to power) so the heatspreder is needed, especially as OC gets rid of your lifetime warranty with manufacturers such as corsair or OCZ.
For the performance increase you get it is very cheap, to get a similar increase if you look at loading times of stuff, fps of stuff etc, you can pay very little to upgrade your RAM whereas you would have to pay hunreds of dollars to get a faster CPU, faster hard drives in RAID etc to get the same increase in performance