Venice Beach is way more than just a beach. Sure you can go there and sit in the sun or frolic in the ocean. The water was reasonably warm when we went there in March—not too warm, but comfortable enough that you could stick toes in without it being freezing and you have to run away. The beach itself and the sand is nice and not rocky or anything and you can sit and watch the waves and the people and enjoy the surf.But Venice Beach is so much more than just a beach. You can walk the length of the beach and see great shopping and art galleries and entertainment and restaurants. The restaurants all seemed fairly reasonably priced, and we ate at a cute little place with delicious french fries that wasn't expensive at all and was right off the boardwalk. There are a lot of unique shops with stuff to buy that doesn't look like it came from a department store—more artsy and cool and not that expensive. You can buy boutique type shirts—I bought a green shirt with ties and sequins and it only cost me about $25 which was a very good price I thought. It's nice because it is stuff you won't find everywhere. There are also little art galleries and things that you can go into and browse local art—a great experience and great way to kill an afternoon.
It's fun to people watch there as well—there are lots of artsy young kids on the boardwalk and you can watch the surfers in the water doing their fancy tricks and be impressed.
Overall, I'd highly recommend that you visit—even if you are not a beach person there is so much more to it with the shopping and the art and the people watching and the surfers. It's a true Los Angeles experience and no trip to LA is complete without a visit. Best of all, if you just walk around and don't buy anything, it doesn't cost you any money (although if you want to park close and you get there a little later in the day you might have a hard time finding a parking spot, or you might have to pay to park.)