Wheels and tires are a good place to start. I went with Mavic Open Pros laced to a Dimension flip-flop hub and an XT front hub. 32 spokes per wheel, but still pretty light. For tires I had a set of Bontrager R4 in 700x25 in my parts bin. I'd look around at options for the lightest tires in your price range that offer puncture protection and don't have poor reviews. Nice tires will ride great, and weight saved there will be more noticeable than other places on the bike. The rear wheel you picked might be heavier than the stock one, weight could be saved there, but it might cost quite a bit to get something noticeably lighter. For the front I would have a look at craigslist and shops that sell used parts, and you will probably stumble upon a front wheel from a road bike that will be an upgrade.
I had a quick look at the specs for the 87 model, and I don't see any super obvious other things to upgrade for weight savings. I'd probably only upgrade other things if you are doing it for a reason like adjusting the fit or replacing something worn out, or if you find a nice part for cheap.