I switched my Raleigh from 27" to 700C, because I like having more tire options, and it's not just the expensive tires either. 27" is a dying size, every year there are fewer bikes that originally came with 27" wheels, rust and crashes, will continue to dwindle the supply. Conversions will also dwindle the supply, and that will make it harder to justify continuing to make replacement rims and tires in that size. If you want a new 27" wheel, even today, you need to get it custom built, and that is expensive, there are few decent tires made in that size, and for some dealers they are special order. I expect in the next 20-30 years you will need to take advantage of the NOS parts to keep that size, and they will not be cheap.