Way past my bedtime... I'm probably missing something here... ignore if irrelevant.
Just to be sure I've got the problem: when you look at the raw feed, you see the enclosure and the image URL, but for some reason you don't see it in the data as parsed by Magpie.
A few thoughts (as I say, perhaps ill-conceived due to late hour).
1. Based just on your variable name ($item), it looks to me like you're iterating through the $rss->items array and grabbing each as $item and then using var_dump() on that.
Have you checked for a $rss->images array? I think that's where Magpie puts images, but I might be wrong.
In any case, try a var_dump() for the full $rss object before running through it for the individual items.
 not wrong I think
2. Assuming you just can't get the image with Magpie, you have the feed XML right? Why not grab the feed itself grep for the enclosure and get the image that way?
I'm not sure how all the pieces of your app/script/site fit together so I'm not sure if #2 makes any sense or if that means you'll just be processing the feed twice, but it's a possibility.
3. Look into another RSS parser.