Nose wouldn't bring much damage to an attacker, likely only anger him more... Solar Plexus would only work if he isn't ready for the strike. If he is, all he has to do is tense his abs and not much can be done. And even if you do catch him unawares, a debilitating blow to the Solar PLexus is hard to deliver. The instep would actually be a damn good spot to hit an attacker, but again, it would take a damn lucky or skilled kick to keep him down. The groin... *grins* Well, most men tend to defend that well.
The best combo I have seen is pulling up your hands in a high guard to defend your face and wait for him to get close. Then pivot your body to the right or the left, your elbow lashing out to catch him in the face, preferably cheekbone or nose. Again, striking the nose is near worthless other than the fact that it will make his eyes tear up. Strike completed, you should be in a good position to wrap your arm around his neck in a guillotine choke and from there power knee strikes to the groin, plexus or ribs. Two or three well placed shots should have your baddie on the ground clutching his preciouses and midsection, where you can finish him off with kicks.
Sorry, it has just been happening so much lately. Slightly annoying.