I can see it both ways. On one hand crashes and bad TPS is not good, but on the other it's not really fair to those that did buy it to just say no you can't have it anymore. Another thing that can adversely affect play is giving away stuff to players not playing creative, it can kind of wreck it for them even though it can be tempting at the time. Although I guess that's their lookout.
I'm not sure on the technicalities of Minecraft 1.7.10 performance, but would it be possible to run two servers on the same physical server without impacting performance? I mean modern CPUs have multiple cores, but apparently 1.7.10 mostly only uses one thread. So perhaps it's possible, though clearly it would also need more RAM and network bandwidth. So I don't know if this is feasible to do without increasing cost. But if it is perhaps there could be the original server unchanged and a new one with no creative. Again, this might not be practical at all, just a suggestion.