I would suggest that you decide on what that domain name is worth to you, not what it is worth to someone else. If you have no intention of developing a website yourself, then the price you can command will always be limited. If they are making a decent offer, I would seriously consider it, as they may just move on to another domain name if you don't respond. Unless you have an unbelievably short and succinct name, then it's value is only ever in the eye of the beholder. Maybe you could consider listing it on a domain selling website and see what sort of responses you get. That might give you a better idea of it's worth. Either way, in my opinion, you're better to cash in sooner rather than later. The days of selling domain names for mega bucks is by and large over, take the win and move on. Or develop the site yourself, build traffic and a database to increase the value that way. Good luck.