You have a long way to go before I would consider a dedicated server. Use what you have now and see how it goes, if you find your forum is slowing down and your membership is increasing then consider a dedicated server but for now keep you dosh in your pocket.
I sell hosting and dedicated servers via one of my sites at
www.serverintelligence.com and have a few customers who use there servers just for forums and they also sell space on to others and recoup costs that way.
Regards.