the value of a numberplate is strictly related to demand. Does anyone want to buy M3 NLC? Possibly someone with an M3 or whose initials are NLC. If you could find someone whose initials are NLC AND owns an M3 you will get a good price, but this is near impossible.
If you think it is worth keeping and you want to sell the car right now, you will need to pay DVLA �105 to retain the plate off the car (�25) and pre-pay for its transfer onto the next vehicle (�80).
You can sell privately (ebay, newspaper, etc) or through a company who will advertise on the internet/newspapers and take a cut.
If you sell privately you should specify whether or not you are including the �80 pre-paid transfer fee in the price.
Have a look on ebay or in the national press, and websites, to see what you think it is worth.
M3 AML �295 Sold in Jul 1994
M3 BMW �12,500 Sold in Nov 1994
M3 CCC �295 Sold in Aug 1994
M3 GAN �4,700 Sold in Oct 1998
M3 HTA �6,000 Sold in Sep 2001
M3 LLY �2,500 Sold in Jul 2002
M3 MMC �295 Sold in Aug 1994
M3 NNA �2,500 Sold in Jan 2003
M3 RCS �3,000 Sold in Jul 2003
M3 RRY �2,700 Sold in Jan 2001
M3 SUN �295 Sold in Aug 1994