No mention of software solutions?
Personally, I kind of like the fisheye view, but when I need to remove it I do so in software. My preferred way of doing this is with an effect in Final Cut. It can also be done in Photoshop, and there are some free apps out there that wil do it (including GoPro Studio - if you use a GoPro which is a MUCH better camera than the stock Vision+)
I don't think any lens ad on or replacements will give you the depth of field effect (foreground in focus, background blurred, or vice versa). There are ways to fake it using shape masks in Final Cut and other editing software, but it's tedious.
If you are looking to add depth to your shots, as opposed to a depth of field effect, then you should probably be tweaking your mid tone exposure in post. Bringing it down a smidge. That always adds a lot of depth to aerial images.