Thank you all for your comments. You've made up my mind. Resale value isn't the main issue, but it is something I wondered about. We don't plan to move again, having waited 22 years to finally live here - where we'd always wanted to but couldn't because of various reasons (children at school, finances, elderly parents still living in London etc.) Houses in our road do sell very quickly when they come on the market so I don't think it will be a major issue if and when the time comes. Anyway, that's my DDs problem, not mine! I'd like a shower big enough to not need a door like yours, Lucca. Less glass to clean!
Thanks again for helping me make up my mind - now to persuade DH that it's the next job on the list!!!