You are confusing "vital areas" and "pressure points" - they are very different things.
Vital areas are larger in scope, since they involve several/many nerves at once, and can have the effect on consciousness as you pointed out. So, the eyes, nose, ears, face, neck, solar plexus, stomach, and groin are commonly accessed (attacked) areas in martial arts. You attack them in some way, say, covering, squeezing, or striking, then they will have varying results - some up to and including loss of consciousness and death.
Pressure points are much smaller in scope and generally involve one nerve point, and can have the effect on a particular body part. And they are attacked either by strike, rub, or squeeze for the particular effect desired; and sometimes, several areas need to be attacked for a desired effect. If you want to release a grip, you hit one area. You want to cause the person to be unable to kick, you attack another area. The problem with pressure points, as mentioned by Sean Duggan, is that effectiveness can vary from person to person, and from time to time, and from condition to condition.
Your knowledge, your strength; the opponent's ability to resist; the opponent being under the influence of drugs, alcohol, or medication; the opponent is mentally unstable, angry, or injured, or is protected (eg, leather jacket); and the opponent's body physiology. Any of this can change the effectiveness of the desired effect when a pressure point is attacked.
In a pressure point, the desired effect is almost always pain. That pain is used as a distraction, a means to release a grip, prevent further attack, etc. But a vital area need not involve pain. Of course it can induce pain (eyes, testicles), but it can also render unconsciousness (neck). Sometimes, a vital area need not be struck: the eyes, for example, can be covered. So can the mouth. You know, like with a cloth. The person can't see or breathe: that's huge. The mouth and chest can be squeezed.
Now, you ask if they are "easily reachable". That always depends on context. For example, you are in a head lock, so your body positioning might be such that the groin or knee is closer than the eyes, and so the eyes are out of reach. You may have your opponent in a head lock, and so the eyes and neck are more reachable than the groin or knees.
You also asked if there are any that don't require much gripping power. As I mentioned, pressure points are attacked solely by strike, rub, or squeeze. Here, power is usually expected; slight strikes/rubs/squeezes will usually not have the desired effect.
But with vital areas, generally, very little gripping is needed, and for cover, squeeze, or strike, little is also needed as well. A poke to the eyes can be very effective, even if you have an injured finger. Any male can tell you that the slightest strike, rub, or squeeze on the testes can induce excruciating pain. The solar plexus is also another area which does not need a tremendous amount of strength to attack. An arm lock needs very little gripping strength; in fact, if you get the opportunity, you can even do it without gripping at all - just use open hands.
I would bet that the gold medal award for the one vital area requiring least amount of power to attack it would be the thumb lock. (I'm not sure the thumb qualifies as a vital area, although it is a surprisingly vulnerable thing) It is versatile, because it's usually more accessible than the eyes (to which I might award the silver medal) only because it's the one body part that extends from the body, and thus allows you more distance to issue than the eyes; and also, it can be used in many instances: weapon disarm, grip release, and other situations might just present itself.
If you manage to get someone in a thumb lock, you can get most people to cry "Uncle!", shine your shoes, and sing Twinkle Little Star with nothing more then your thumb and index finger, all the while using your other hand to play solitaire on your smartphone. Here, of course, virtually no gripping power is needed at all.
Nevertheless, when you train in martial arts, it does well to train and condition the whole body, even small joints. For example, I regularly compete or participate in demos. And in them, I break boards with fingertip. Is it needed? No, not really. But, my hands become very rigid, and an eyeball or throat for a target is easily dispatched, because I train to break boards with the fingertips.
EDIT, To clarify:
Pressure point effectiveness varies from person to person, because some people are able to withstand the effects of PP. Also, some people's nerves are not unlike veins and arteries: they move. So if you apply a PP to an area, if that person's nerves or skin moves, you will have a harder time applying the PP.
As to condition to condition, if someone is injured and a nerve is cut off from the brain (eg, a deep laceration), or the area is significantly traumatized through blunt force, then that person's ability to sense the PP effectiveness is significantly weakened.
And as to time to time, there are times you simply cannot apply that PP. Perhaps you are too fatigued, or maybe you distracted. Maybe a PP requires a rub, but that PP lies beneath a jacket - that would give protection to the PP area. Maybe you are wearing gloves or have your hands otherwise occupied (with a grip, a weapon, or your own hands are injured).
There are many who doubt the efficacy of PP. Perhaps they've never felt them being applied real time. Perhaps they've seen too many charlatan videos on YouTube. Perhaps they've not been taught properly or have not had much experience. Maybe they're not aware that they are already using PP. Any time you apply a lock, you often attack a PP or VA. Or perhaps they have a body mechanic that makes them more resistant to them.
The study of PP is not something that can be done in a class, or a couple of classes, or even a couple of weeks of dedicated practice. Once you understand how the nervous system works, you begin to understand how to apply pressure points - and that can take years of study and earnest practice.
While you study pressure points, be sure not to forego all of your other training. Pressure points - like any technique you are taught - should always present themselves; you should not go looking for them. You may live an entire lifetime of fighting and never once have a situation present itself with a juicy pressure point handed to you on a silver platter. The study of pressure points should lead to many discoveries about how the body works, so even if pressure points don't work well for you or don't seem to yield the results you were expecting, you still should have learned a great deal about other aspects of the body mechanics that are useful in a martial arts (or healing) context.
