I lived near Irvine for a couple years after college and have family and friends in the area, so I will try to address a few questions about housing and lifestyle.
If you are looking between Irvine and San Diego, I would check out San Clemente and Oceanside. San Clemente is a very laid-back town - full of older beach cottages and surfers. Oceanside is a bit bigger and has more of a military presence (lots of Camp Pendleton families live there). Also there is an amtrak line (Pacific Surfliner) that runs from San Diego all the way to San Luis Obispo with stops in Solana Beach, Oceanside, and Irvine. the Irvine stop is not at UCI (unfortunately), but the school has a sustainable transportation center that could help you figure out how to get from the train station to school. The train follows the coast and is very relaxing and beautiful - not a bad way to get to school.
For people looking closer to Irvine, it depends on your age and what kind of lifestyle you are looking for. The Newport peninsula is nice because you can ditch the car and ride your bike around to bars, restaurants, the beach, etc. The area between 30th and PCH is known as the war zone and is known for young people and parties and the area from Balboa to 15th Street is mellower and nice for couples and people who are over the party scene. There is a great little coffeehouse on 31st which has good food and atmosphere (including the requisite mismatched furniture and resident cat) and a few pretty good restaurants (my favorites are Ho Sum Bistro for the mixed salad and the homemade pasta at Il Farro). There is also a new shuttle from Newport Beach to UCI. The key with this area is that most of the homes are owned by individual property owners so the prices vary widely and bargains can be found. The two best ways that I know to find the best and cheapest places are to drive around and look for signs or a website called West Side Rentals. It has rentals in Orange County and Los Angeles.
There are other good towns, depending on how much you want to drive. When I just couldn't take Orange County any longer, I moved to Long Beach, which is a really great, diverse, interesting city. Good bars, coffee shops, restaurants, museums, etc. and is close to both LA and Orange County. It would be a bit of a commute to Irvine, though (30 minutes without traffic).
For the vegetarian/vegan, Orange County is not as easy as LA or the bay area to find veggie fare, but it's probably easier than many other places. There's a Veg Out guide for Southern California that lists lots of places to check out.
Hope this is helpful. I agree with a previous person who said that Irvine isn't the best cultural mecca on the planet, but it does have good qualities and close proximity to the beach, the mountains, the desert, and great weekend destinations (Los Angeles, Mexico, Las Vegas, San Diego, Santa Barbara, etc). You could certainly do worse.