Combat Casting is definitely worthwhile, particularly if Skill Focus is restricted to +2.
Put it this way: a 1st level character with maxed Concentration and 14 Con has a Concentration check of +6. He fails to cast his first-level spells on the defensive 45% of the time. With Combat Casting, he only fails 25% of the time. In other words, you roughly halve your chance to fail.
It actually performs fairly well throughout most levels. Consider the chance to fail casting one's top-level spell on the defensive at the following levels. The figure before the slash is the %chance without CC, the figure afterwards is the %chance with CC.
1st: 45/25
2nd: 40/20
3rd: 40/20
4th: 35/15
5th: 35/15
6th: 30/10
7th: 25/5
8th: 20/5 (using optional 1= -10 rule)
9th: 20/5
10th: 15/5
11th: 15/5
12th: 10/5
13th: 10/5
14th: 5/5.
15th+: 5/5
In other words, up to 13th level, you are getting a discernible benefit. Up to around 9th level, that benefit is fairly significant, especially given that the higher-level spells are going to be more significant in terms of game impact. Creating a 1st level caster I'd be more inclined than not to take it (especially if human). Taking it at 3rd will get you some utility. I'd be less inclined to take it at 6th, and would never take it at 9th, by which point most of its utility is spent.
I will agree with Endurance. I have never ever seen this taken by anyone, nor have I given NPCs it. Toughness is of some use for low-level wizards, and Skill Focus can be useful for NPCs, but Endurance is very rarely used indeed. Even career foot soldiers would be better placed taking Toughness, Power Attack/Cleave or Improved Initiative.