Do vehicles have any impact?
The main reason for decay and Maintenance Supplies is to keep server performance at a stable level. For that reason, anything that can impact performance can theoretically have an impact but there are measures in place to mitigate the obvious cases of griefing.
To be upfront though, it's version 1 of a brand new and complex system. If there are issues please let us know so we can iterate in the future (though please don't take this as a promise for any particular change being made).