The railway I volunteer at, the Isle of Wight Steam Railway, fairly recently became an Accredited Museum under the Arts Council scheme. This is for the whole railway and not just the museum per se. It took a lot of work to achieve this and continues to do so but is beneficial in terms of conservation and historical study. We have consulted with professional museum staff including a meeting at one of the august London institutions.
Nothing is perfect and I do get exasperated that it is so difficult to experience a branch line type train worthy of the name except, perhaps, on much trumpeted special weekends.