Before providing a definite answer to your question, it would be necessary for ANY attorney considering this matter to review the precise language of both the easement and the road maintenance agreement. Given that I have not read either, my tentative answer to your question is based on general rules governing easements, any one of which could have been rendered inapplicable upon agreement of the parties by the language of the easement.
There are three long-standing rules governing easements that are implicated by your question, the application of all three of which look to lean in favor of your use of the private road. The first rule of thumb is that the granting of an easement does not effect the ownership of the property at issue, nor the owner's right to use the property covered by the easement in a manner that does not hinder or prevent the use of the easement by the party to whom the easement was granted. So, for example, if I granted a utility easement to a power company to erect towers and string high voltage lines across my pastures, I could still graze my cattle on the land covered by the easement, as such use would not hinder or prevent the power company's easement use. Thus, your use of the property as a road would be entirely consistent with the use you (or a previous owner of your property) granted for the easement. Your use of the land as a road would not hinder or prevent the others' use of the easement land as a road.
The second rule of thumb applies to the traditional definition of an easement. Most hornbook authority would define an easement as "the granting of a right to use or enjoy another person's land for a particular purpose THAT IS NOT INCONSISTENT WITH the general property rights of the owner." The right to occupy the land and the right to traverse the land are both part of the property owner's general "bundle of rights" that he holds as a landowner. If the road easement prohibited you from using the road, it would prevent your right to traverse the property, a result inconsistent with your general property rights, and would likely be considered invalid.
The third easement tradition relevant to your question is the general rule that maintenance is the responsibility of the easement recipient. Maintenance agreements are usually only executed when more than one person/property is granted the easement--for example, when an easement is granted over the same piece of land to both the electric company and the local cable company to bury utility lines under the ground, the utility and the cable company (but not the landowner) will execute a maintenance agreement for that easement. Usually, the assumption of maintenance obligations is part of the consideration, in addition to cash or other payment, that is given by the recipient to the landowner in exchange for the easement. In your case, while it would be reasonable for the parties to the current maintenance agreement to be upset should another 10 parties be granted an easement over the same land without joining the maintenance agreement, it would be unreasonable for those parties to be upset over your (the landowner's) use of the road without participation in the maintenance agreement.
Again, these very broad rules can be turned on their head by the language of the easement and maintenance agreements, but so long as the documents do not expressly contradict these general standards, you can probably use the road even though you are not a part of the maintenance agreement.
As a side note, your plans to erect a gate on the private road are fine, assuming all parties who have easements can use the gate (have keys or the lock code, etc.). If you put up a gate that prevents their access or use of the road, they will likely have grounds to sue for enforcement of the easement.