TLS,
I checked your ISP's website. You're connected at 10Mb/s, and the ISP offers speeds up to 25Mb/s. Divide your download speeds by a factor of 8 to convert to MB/sec. It looks like the 25Mb/s service represents a $30/month premium over your current service, or ~$400/year after taxes/fees etc.
You would have to decide if it's worth the extra money to you, but a 150% increase in speed for a ~60% increase in price seems reasonable from a purely mathematical standpoint. Keep an eye on your transfer speeds and see how often you're hitting the transfer speed ceiling. If you're constantly bottle-necked at your current speed, then perhaps an upgrade is in order.