Of course most of the general public wouldn't know a 117 from a 17, 47, 70 or 170. They are all just trains, even when they are not. The heritage DMU is shiny so, would probably be considered newer than a work worn 150 or 158. Days out to London can be covered comfortably as they used to be by leaving Wareham after 09.30 I think it was on weekdays, earlier on weekends. Get back about 2230/23.00. It is only in winter when that is less desirable, summer is fine. However, I still think Swanage has no intention of running these trains all year round or even in summer.
But part of the point was to provider a commuter service, not a glorified tourist train.
And the general public are savvy enough to know the difference between a 60 year old train and a 20 year old one - and if they don't the local media will no doubt help them make that distinction.
I maintain if it's about providing a clean, reliable, comfortable, environmentally friendly service than a newish Volvo / ADL / DAF bus beats a 60 year old DMU on each of those every day of the week - it's also more flexible and more cost effective.