Good to be here. I am a beginner kajukenbo-ka (sp?), but a journeyman martial artist. Thanks for reading my two cents worth . I believe the foundational base for MMA and self-defense does not necessarily have to be the same.
With self defense applications, I think you need to go with a striking base. A lot of the problems I see with grappling is that there would be too many X factors when applying it to a self defense situation. Mobility, and perhaps the necessary speed to escape, are lost. As mentioned earlier, you lose the ability to defend against multiple attacks. There are no mats and rules, so you'll more than likely be on concrete with your opponent biting you in the calf if you ever try an armbar.
With MMA, you can go with either, as natural strengths and weaknesses will differ. For example, I'm naturally a better grappler than a striker. In fact, I consider myself a horrid striker. So I would probably benefit more from using grappling as a base, and focusing more on learning how to defend a striker than learning how to strike.
However, I think what is true for both MMA and self-defense is you must be able to take a hit, which was touched upon by Todd Reiner earlier. Tyson said it best: "Every fighter's got a plan until they get hit in the mouth." If you don't have the composure and discipline to take a hit, you will panic and forget your training. Once the training is peeled away, all you have left is your instinct. And for some people, that instinct may tell them to RUN.
One recent example I can think of comes from Pride FC's Total Elimination 2005. In the bout between Sakuraba and Yoon Don Sik (an Olympic caliber judoka), Sakuraba landed a good combo on Yoon in the first minute of the fight, Yoon panicked, went down on all fours, and covered up, then Sakuraba went in for the kill. Fight over.