I dotnt think it is worth more than the $300 you already paid. You need to develop quickly and try to get traffic to it so you can try to earn at least $300 a year in revenue from it. Just hanging onto this for 5 years is going to cost you $1500.
I have to say too that you should develop it. I think if you can establish some good rankings your off to the races.
Blogging about the current trends and best practices in the niche might be your best bet if you are not the expert yourself. Let your users and readers provide the content.