Looking at it, I'd say it's definitely worth finishing. It seems most of the way done (the engraving looks finished, for one thing), & any additions (like the wooden shed) won't add much to the weight. It could be a great centrepiece, once finished.
But if the weight makes it a problem, or just uncomfortable to use, then... Could you maybe drill out some of the gasbeton in the columns to reduce the weight? Don't finish it unless you'll be happy using it.