The biggest problem when buying an older van is getting a good one, most will be x work vans that will have had a hard life and in need of a few quid spent on them, even then there is no guarantee that they will be reliable, I bought my van from new, its now going on 13 has been well looked after looks like new and has around 35k miles on the clock, hopefully it will do me for another 5 years until I retire, at that stage it will have cost me around £800 a year to buy and maintain.
Its the upfront costs that make some think that a new van is a false economy.