If you have a working system now I would advise doing other things before swapping out logic boards. If you have a dead logic board then it's just a matter of what your willing to pay to get your system running again. Also, you also run the risk of not getting a board that will work in your given system when you use something other than what it came with (series release).
The small incremental clock differences between 2.1Ghz to 2.4Ghz for the fastest Intel Core 2 Duo CPU used in a MacBook in this series, is not enough to offer enough performance benefit given the costs.
A better direction to improve performance here would be maxing the RAM out, a faster spindle HD & larger size, taking out the optical drive and installing an SSD in its place. And better still swapping the HD & SSD around so the SSD has the faster SATA Vs PATA connection.