I was in your shoes once and I think I polled the DIS as well. My DD was so young, and so set on a guinea pig that we ended up getting her one for Christmas. It's not a course of action I'd recommend for everyone, but we're a rescue-type family, and DD at age 6 was a big part of it - we took the chance. That was ten years ago, and I have two other DDs, so naturally we acquired more and have one still. Our first guinea pig lived for five years.
They are pretty good pets, and I have to agree that for small animals they have big personalities. They're sociable and they will make demands on your time, and let you know when they feel ignored. At the moment we have just one, but she gets a lot of attention. It's good to give them the maximum amount of cage space you possibly can. Check
http://www.guineapigcages.com/ for some great ideas. A big space gives them running room to exercise; it will accommodate another piggy if you're inclined to add one, and also, with enough space they will tend to use only a part of it as a litter box, which cuts down on overall maintenance.
We use Carefresh bedding, which does not smell, and I would never go back to wood shavings. I'm thinking about regular delivery from Petco but having signed up for it yet. Our piggy has food pellets all the time, timothy hay in the morning, and "supper" at suppertime, meaning fresh carrot, cucumber, apple, celery, grapes, green pepper...whatever. By now it's just a habit for me to collect cucumber peels and veggie pieces after making a salad or stew or something, and not really an extra expense or inconvenience.
Last time I had to take one to the vet was six years ago, and it was considered an exotic pet visit - a little more pricey, just FYI. But we've only ever had two vet visits for all five piggies we've had; they rarely get sick.
Hope this was helpful.