My parents live near Brighton, so I will naturally tend to drive to Sheffield Park if visiting the Bluebell as I'd be staying with them. The only time I see myself using the mainline link is if I get a railtour, tbh.Yep, main aim was to visit Sheffield Park, so I drove there from Southampton and then got the steam train to East Grinstead and back. Thought the main line connection was pretty cool, but would be unlikely to use it if I wanted to go on the Bluebell railway again.
I think the mainline link has been valuable for the Bluebell - the extension project itself gained a lot of publicity, the tracks are at least visible from the station, and it has also opened up several commercial opportunities with railtours, Steam servicing (Clan Line has visited the workshops at times), loco exchanges, and also mainline training operations with tampers and so on. Passengers aren't the only source of revenue a mainline connection gives.