Well, I guess it's making sense why you're trying to optimize for space if you're running from a hosting account... but I'd still have to ask why that's your main consideration. I'm guessing that if you're trying to get more people to use your site, you're going to need to add stuff for the users, not for you. (and your users probably aren't going to be discussing the benefits of data storage techniques ... well, the might be, after all, I'm doing it right now).
Given what you've mentioned, I'd probably store the metadata in a database, just because I would feel comfortable coding with that backend. However, I would try to make sure that I/O is encapsulated, so that I could change the storage system at some later time, if I wished. (or I could recycle it to be used elsewhere)
But I'm going to have to agree with your decision to stop using WWWBoard. I mean, it's 19105, and you're running a program which tells you to chmod a directory to 0777. It was 'ast modified' in 1995, and is still in 'alpha'. (although, the copyright is marked 2002... I guess he knows what the important things are to update.) Hmm...okay, I should probably stop flaming Matt's Script Archive, or this post will go on for pages. -- I will give him credit that it was very nice for him to want to share with the public... and that's about the only nice thing I can say about it.