In my most humble opinion, I should tell you to wait until Garmin solves some serious issues with the Montana 7xx(i) and Garmin express. I just bought a 700i and have been trying to fix the mess Garmin express created. Just wait until you don't see any complaints any more.
It really depends on how you plan to use your device. If you want to have a camera available on hand to take photos of things you see while traveling and want it geotagged and waypointed on your device, then it's actually very useful. There are a number of applications where this would be more useful than a phone - for me, it's for marking specific trees, plants, buildings, trail markers, signs, and other interesting/curious things I find on the trail, and having it automatically placed on the same map as my tracks. I also like having some redundancy with my phone's camera just in case it runs out of power.
The quality of the 750i's camera does have fairly poor low light performance, but its daylight performance is reasonably good. The macro focus is pretty good. The focus mechanism is actually pretty good. It doesn't have an OIS that is destroyed by vibration, unlike cell phones.
If you don't really ever take pictuers of anything on the trail that would benefit from being automatically integrated into your Garmin's mapping ecosystem, then I agree, it's probably not worth it.
I recently got the 700i but now wish I had gotten the 750i for the integration of images. As was previously stated, depends on what you want to do with it.
