I agree. A Lagg gives more bandwidth but no speed increase so if you are not filling 1 port there is no reason to add a second port.LAG only provides real benefit for multiple users accessing the NAS at a single time. So it would be good for a server facing the internet where thousands of users are accessing it. LAG can be used to increase data transfer between two devices that both support the higher rate - such as two 1Gb/s ports on a router LAN switch and two on another LAN switch that both devices support LAG on. All that does is shift the bottleneck elsewhere in the network - perhaps the router LAN to WAN connection or the LAN switch connection to a PC over a single Gb/s port.
Oh, Ethernet cables only need not exceed maximum length whether they are the same length or not in a switch makes no difference.