Wonderful idea, but I expect it will be underpowered for its size and weight. Each component has a casing, meaning a lot of space is being used by by non-functioning casing. Add to that the oversized connection pins, and you will end up with a phone bigger than the competition with nothing close to their power.
I actually find that phones last pretty well except for the battery so long as you avoid drops. I am just a sucker for the latest and greatest, so I tend to upgrade.
Also, if you are on AT&T, Verizon, or Sprint, you will likely upgrade anyway since you are entitled to it if you want to stay with your carrier for another 2 years. You also pay more for your plan, whether or not you take advantage of phone subsidies. At the very least, you should upgrade, paying $200 bucks for a new phone, and then sell the phone for $600 brand new if you don't want it.
If you are on T-Mobile, this idea makes sense since you are not paying extra monthly to cover subsidies.