I think it depends on the person really - some people wear wellies regularly, others don't. I'd say to get some if you feel you might wear them at some point and that they'll come in handy, but if you don't get any, I don't think it will be the end of the world.
I've lived in the UK my entire life and although I used to wear wellies when I was a kid, I haven't owned a pair or worn any at all in about 15 years. I live in a large town near the countryside (I only have to walk 5-10 minutes from my house and I'm in the fields, but the city is just a few miles away), but I rarely walk anywhere where I would need to wear wellies. If I'm going walking in the country, I usually wear either trainers (if it's dry) or my hiking boots.