If you love the 4-inch iPhone, but have been tossing around the idea of switching to the iPhone 7 Plus because of the awesome camera and super cool hardware feature, consider this: Why are you still using the 4-inch iPhone?
If the answer is that you have small hands and are afraid that the iPhone 7 Plus is too much to handle, literally, then you might want to stick with the 4-inch form factor, or at the very most, upgrade to the 4.7-inch iPhone instead. I can say from experience that the iPhone 7 Plus is difficult to use for long periods of time and I find myself not wanting to pick it up as often.
If the answer is convenience (the 4-inch iPhone just fits better in my pocket), then you should think about an upgrade. As annoying as it was to squeeze the iPhone 7 Plus into my tiny fanny pack or even hold it because I didn’t have a pocket to fit it into, I could have gotten used to the size. I would probably have eventually purchased a larger fanny pack, or move onto some other bag, to keep the iPhone 7 Plus in. Though it is less portable than a 4-inch phone, it certainly shouldn’t be the only reason you don’t upgrade.
If the answer is cost, then you might want to look into the iPhone 6 Plus. It has a ton of awesome hardware features that the 4-inch iPhone doesn’t, like 3D Touch, more storage capacity (up to 128 GB compared to 64 GB on the iPhone SE), a 5MP front-facing camera, and more. It costs $120 less than the iPhone 7 Plus model and you’re getting a whole lot for a whole lot less.