To each their own, for sure. For me, the billet parts and upgraded hoses are a set-and-forget solution, for the kind of driving I do - towing a heavy trailer long distances in hot southern weather.
Another factor I consider is what the result of a failure of any failure-prone part would be. In the case of the tees, it has the potential to ruin my day at best, and at worst put me and my family in danger. I can think of many places where blowing a coolant tee would be a serious problem. To be clear, I agree that the likelihood of OEM tees failing is low, but the real cost for me is getting in there and doing the work to replace them. And, I know that I plan to keep my 2012 for another 10 years, so if I can take the likelihood of failure to zero for $100, more or less, it's worth it to me, but might not be to you, and that's okay.
It's a similar cost/benefit analysis I use when replacing something like a fuel pump with OEM vs aftermarket. The OEM pump is shown through the experiences of many here to be more reliable than aftermarket pumps, but costs $200 more. Since it's a PITA to do the job and the consequences of failure are significant, I'll spend the money for the OEM pumps on these trucks.
