You have a way in the Customer Portal to separate Open Requests from Closed Requests.  That's very good.  It would be extremely useful (and I think you'll agree, being a software company yourselves) to separate Enhancement Requests as well. 

 Customers, especially engaged ones, like to suggest improvements and want to ensure that those are not lost.  Also, these requests shouldn't necessarily be "closed" until they are fulfilled.  Some may never get fulfilled, of course, and your response to the suggestion would indicate that may be the case.  

While these requests are open (which may be forever) they really don't fall into either the closed request or the open request categories.