Alex - the arse is falling out of the used E36 market, believe me, Ive got one in my garage!
Firstly the colour, Boston Green isnt a great resale colour, but the low miles is a good selling point. Depending on spec, Ie leather, colour of leather, Climate (some Evos didnt have it), ESR, blah blah you should sell it for 15-16k - also depending on the amount of previous owners. Have a look on www.autotrader.co.uk and see what they are selling for.
The E36 market is strange at the minute as there are some Evo's going for 12k, and some for 20k, a 3.0 Cab will now only fetch 13-14k - even a minter!!
Evo's are flooding the E36 M3 market with the 3.0ltr now being the rarer car but they are going for 9-13k!!
If yours is as nice as it sounds I dont think you will have any trouble but be warned, a freind and myself are both selling and both cars are very clean examples - niether of us have had much interest as there are so many for sale!! - beware for tyre kickers and thieves!!!
Iam already loosing a fair bit on mine but it needs to go so I can put the deposit down on my new one!!
Try a higher price then come down, rather than just sticking it in a a lower price.