30 and 100 .... cannot tell you the difference except for numbers. hahaha.

If you are a single user there is not much difference if you consume media only by yourself. If you have 2-3 person then there would be lags. If you wifi, won't be much different. Most wifi still on B/G/N standards.

If you do movie downloads or anything that does large volume of data downloads like HD movies or stream HD content, then 100mbps does make a difference.

If you have low speed line, then yes. A good router will manage traffic the best compared to stock ISP router. Mainly the damn processor is the one that does this.