I have a suggestion and I'll post that here. I would like to clear something up before that.
A Gantt chart is not a project plan. It is a list of tasks to be done, usually with the resources. It could be used as the project schedule. A plan is much more than that. Its one of the project management myths a lot of companies without strucutered PM propetuate, that a Gantt is a project. I've run projects that never got near a gantt chart. Right now the only reason I keep around MS Project files is for showing the execs why they can't have a product release in only eight weeks.
Okay, if I might replace "plan" with "schedule", here is my suggestion.
Go for Option 2: For a number of reasons.
1- Mental sanity: You are effectively the program manager. It's not your job to track the individual projects. Your job is to see if things are on track and to work with a project manager (leader, whoever is the "point man") when a problem rises up that threatens that project.
2- Time: You'll spend all your time reporting and none solving problems.
3- Errors: If you have one shared Gantt file with many users, you increase risk someone steps on someones changes. IF your master Gantt is separate from the project Gantt, you can quickly get out of sync.
I'd take it a step further and ask what you need a master gantt for? Gantt charts are not typically good for reporting up. You can spend a lot of time massaging it to make it look good. If you are just tracking major milestones and are manually inputting that data into the master Gantt that could be a waste of time. I currently use a simple Excel file that has all 30 projects we currently use. I have the major milestones as columns and dates in the cells. I color code the cells to quickly show status and have a notes column for one/two sentence status. 90% of the time I just use this. When I really need a strong "presentation" I copy this into a ppt deck I have that is designed to be an exec dashboard.
Ask yourself who needs the data, how will it be used, how often is it needed (when) and why it is needed. Often you can go with a much simpler solution.