I wouldn't wash, but I don't usually prewash anyway.
The one kit that I have put together, I won in a raffle, and I really enjoyed sewing it together because I didn't have to think about the pattern, or the fabric choices or any of that. I just pulled it out one time when I didn't want to have to do any planning. It wasn't something I would have picked out and I donated the finished quilt to raise funds for adoption. I had enough of all the fabrics except the backing.