I would hardly call pressing on the prostate "a man's G-spot." Seems like a forced comparison to me. The impression I get from men who have been anally penetrated is that it "feels good" but doesn't create the trembling, flailing orgasm we see with women and their G-spots. A woman whose G-spot is mercilessly triggered over and over can temporarily become completely idiotic and limp; I've never heard of any such thing for men who receive anal sex.
Whether prostatic stimulation is worth the risks associated with anal sex is up to each man to decide for himself.
As for licking the perianal region, I really have to advise against that as a medical student. So, so many bacterial and viral diseases are transmitted fecal-orally. Normally you get them by not washing your hands after wiping your butt, touching door knobs and stuff, and then other people touch those too and then put their fingers to their lips or in their mouths (like when eating a sandwich and licking off some sauce). But if your sex partner has gotten sick with something and doesn't yet know it, you've got a damn good chance of getting sick yourself if you lick his or her asshole. You'd be better off kissing them in the mouth, on unbroken skin, or in the vagina. If you are going to lick your sex partner's perianal region or stick your fingers up his or her butt and then place them to your eyes or mouth, I would at the very least strongly urge that you only do so with a dedicated sex partner; that they clean their rectum well (by sticking their fingers up there during a pre-sex shower and cleaning out any microdebris); and that you be in good health (and not be somebody with a weak immune system, like an AIDS patient or an organ transplant recipient).