VLAN won't help - its still sharing the bandwidth.
An Independent wifi setup would ensure that there are no traffic issues.
The problem is really only an issue if you are doing high bandwidth stuff - transferring files, streaming video, surfing with a really fast ISP connection, etc. All of these are sharing the bandwidth. Ethernet uses a listen before talk approach to avoid data collisions. If something else is being transferred, your packets could be delayed... A little would not be noticeable, but depending on how many computers are waiting to transmit, the delay could be enough to matter.
RM