You don't need it now, but you never know what the future will bring. You don't have to use all the space on a 32, 64 or 128GB device, but you can't use storage space that doesn't exist if you want to go past 16 on a 16GB device.
I'm beginning to get worried that the 64GB Plus is the one that will be in highest demand and there may be an issue getting them delivered. It's the one I'm getting. Oh well. I guess I HAVE to get up at 0230 on Friday to preorder.
Same boat here, but I think the 16gb will be in the most demand. Historically, Apple has sold the most iphones with 16gb capacity. Add to that the $100 increase for the plus and I think people will be all over the 16gb