It's a place everyone should go to at least once in my opinion. It can appeal to many sorts of people. I am the kind that tends to dress up for them along with my group of friends who do also. I just enjoy doing it but the fun of going is that no one has to dress up. It's just a nice time and I would have just as much fun going not dressed up and I have gone just in regular clothes when I was in school.
The fairs offer an experience you do not get in other places and so many states have them (I hear there is one in Texas that is all year). Half the fun is also seeing costumes people made sometimes by hand at home. I make my own chainmail armor and it just adds to the fun of going being able to show something you made. If the guy I was dating said: "Hey let's go to the ren fair." I would more than happily go and may offer to make a costume if he wanted me to.
Some may ask "But I don't dress up and I am not into history so why should I still go?":
No one should force you to go anywhere. However, I would still say give the place a chance because the food at the Pennsylvania one is amazing. You may know some theme parks have bad food but the ren fair is very different in that aspect. The one in PA also has wine and beer. I do not condone over drinking and such though. I suggest looking up one near where you live and doing some research on it. therenlist.com is a good place to start.
That's all I have to say on this for now. I plan on going this year and twice or more if I can.
Have a nice day!