Titan's are absolutely worth it, but only at their launch date. You get 8ish months of tippy top performance, then about 14 months of +/-5% top performance, rinse (sell it) and repeat (buy next gen titan).The Titans are never worth it for gaming. You'd have been just as well off with the 780tis and 1080tis, respectively.
If you don't pick it up at or near launch, your absolutely right, but remember that Pascal is going to be old news as soon as Turing/Volta/Ampere launches late this year, and that 1080ti will likely be beat by 30% or more. If the cycle is consistent with history, the Titan GTX will be launched 5 months after, and the Ti version will be another 8+ months.
As for motherboards, the one I regret is the Sabertooth, died on me and now I'm dealing with Asus RMAFML. Love their ROG line so far, never had a problem.
Edit: Yes I would take a new GPU that offered %30+ performance. Yes I considered Titan V, but its really not a consumer card and the Prosumer features would be wasted on me.