One trick I used before was to create resources and leave them unused until they are allocated, at which point I create another one to top off the pool of pre-created resources. A stopped cluster takes up disk space and nothing else and this is an easy solution to the user experience issue.

Of course, hardening multi-tenant clusters is also needed. Even if the use case requires resource partitioning, there are use cases that don't and keeping one friend from stepping on another's toes is always a good idea.