Although I didn't go last year, I went the 8 years running before that with a group of my mates. The best way to do it very much depends on what it is you want from the day out. I'll be honest, you'll have very little idea what's happening in the race unless you listen to the radio or rent a kangaroo TV, but then it's similar to rugby in so much as you go to the ground more for the atmosphere and watch TV for the view and replays.
The last time I went was the first time I'd paid for reserved seating having gone general admin before that. We found that as they've developed the track they've binned off the general admin areas. It had reached a stage where we had to enter the track at about 5:50am carrying a load of deck chairs to have any chance of getting a reasonable view (I'm not being pedantic here. Much later than that and you'd be behind thousands of people with little chance of seeing the track.
It's very different to most sports in that you're allowed to take food, drink and chairs into the circuit. If you don't you'll pay ~£4 a pint and about £7 for fish & chips. If you're in general admin you will need chairs.
Personally, if you're going with family and it's your first time I'd definitely pay the extra for the reserved seating. It'll allow you to walk around the track and see the teams' display stands. Some of the stuff on show is very interesting. Last year's cars, technical demos and of course pit girls, although there's a lot less of that kind of stuff these days - on my first visit at 14 years old I was given free packs of cigs from lots of scantly clad lovelies. I was too young to appreciate it
Feel free to drop me a PM if you want any more specific info