I've had nothing but good times at these occasion with my wife's family. 

The things I don't like is:

1. The transport nightmare

2. The duration, I am not sure why Spring Festival needs to be a 3 week event, when it is just two nights something special is going on. I'd rather spread the time with the family into several shorter visits. 

3. I honestly cannot tell the Spring Festival dinners from any other dinners. 

The things I like:

1. It is usually very relaxed, sleep late, eat, talk with the family, eat, go for a walk in the park etc. My wifes family is great and very understanding of my strangeness. 

2. The crazy fireworks (... for one or two days, the weeks before and after not so much) 

I agree it would be a great way to see a part of China that is otherwise not accessible to most people. Be positive, bring some presents (ask your friend for suggestions on what, how and when) and remember that it might be equally awkward for them. 

Does the place you're going have any touristy things, is it a small town with nothing to do. Consider how long time you can stay without being bored to death. 

One extra concern would be if you are being exploited as a face-buying white monkey. 

But, go for it. 

When I went with my wife to Hubei for the first time my Chinese really sucked, I'd been here around 1 year and we went back because of a family emergency, meeting the family for the first time made it harder but the family are all nice people and made me feel very welcome.

If you need some preparation for the questions just go have a few foot massages beforehand, the girls there will ask lots of similar questions. You could even request a girl from the same province you will visit as to adapt to the accent for easily.

The locals there will be speaking their local dialect, so watch out for that but they will be able to use mandarin also, depending on if they have ever left their hometown and traveled for work their Mandarin may not be that good and could have a heavy accent.

Don't worry about being the only foreigner there, enjoy being a celebrity. They will be eager to meet you and if you can speak Chinese they will be very surprised and happy.

Lastly, just enjoy it and relax. Hometowns are awesome and you can eat some really authentic Chinese food, not the crap they serve in the restaurants/hole-in-the-wall-joints in the city!

Check out whether or not they've got a shower, toilet, hot water, a bed, etc..  Take a sleeping bag.

Or do what I'd do, and politely decline.

  I don't do get-together's anymore really, which is sad but true; i've done more than my share here and unless you're with an English speaker who's willing to give you all of their time you inevitably get stuck with your thumb up your arse, looking like a plum with nobody to talk to. I've got enough Chinese to join in now, but it's still not enough to fully join in on a casual and fluent level, so unless i'm put at the children's table, I once again finding myself stuck with my thumb up my arse, looking like a plum. Not really my idea of a good time. My interaction with 'the real China' is now conditional on being able to say "Cheerio, i'm off" with no more than a five minute window between decision and extraction. Having said that though, if you make it clear to your friend that you'd rather not get a smell thumb and he/she is willing to keep you company on your visit, you'll probably have a really really nice time.

dunno how it is with just a friend...

i went to meet my gfs parents this year for new year the first time. it was awesome, they treat me like a king and ignore my gf

the city is kinda rural and countryside so nothing to do there. What you will do there 2 weeks is following:

every day visit another relative to have food with them and play mahjong (i really love it now lol, mostly dont lose or win money)

otherwise only talk and thats it.

chinese new year is pretty boring

I spent one Spring Festival with my wife's family
 

The Good
   * Spending times with the in-laws in a relaxed atmosphere. We play card, chit-chat, walk with my wife and her mom in quiet country-side.
   * Lots of beer
   * Good time to read books

The Bad
   * Transportation with Chinese Characteristics, but worse, the true meaning of chaos.
   * The in-laws home is a cube with thin bare concrete walls, all window opened. It's *cold*. Because it's cold, no shower.
   * Share the bed with the brother, the uncle and whoever is too drunk to go back home