NAS are meant for backup so your network speeds typically aren't going to be a major issue. Most people run the backup automatically over night.

You're likely bottlenecked by the HDD read/write speeds anyways. I wouldn't upgrade the router solely for the NAS unless you're router is ancient or something. The NAS only supports up to 1 gigabit speeds anyways out of the box.

Though, it does support link aggregation (2 network cables) so you can either set it up for redundancy or a 2 gbps connection. If you want to use this feature you'd need a router that supports link aggregation though.