Is there any benefit for me to use OmniPlan in addition to OmniFocus
 

I would consider myself a power user of OmniFocus and it has served my needs very well. But I can't help but to think I am missing out on the some project management if I used OmniPlan for some of my larger projects. However my projects mainly consist of organizing my own workload and have hardly anyone else involved. Is the only benefit to OmniPlan to OmniFocus is the ability to monitor multiple people?

A couple of benefits would be the ability to monitor multiple people, as well as being able to track the costs of all of your tasks and seeing a visual representation of your project. Depending on how many tasks you have to do, OmniPlan can also help you determine how many tasks can be completed in your workable time budget.