You can have a huge pipe, but if the server can only send a few packets per second, you will not benefit from your connection speed.
A faster service is useful when you download a lot, and/or use P2P with many downloads going at once. Even then it's a matter of finances. Can you financially handle the additional $25? Of not, don't do it.
The question is rather simple: Do you need the increased speed, and is it worth the additional cost per month?