Defog was stupid that Gen; don't tell me that you would be using that.
Starmie was, undoubtedly, one of the best Hazard Controllers in Gen 4 OU.
And, about the sweeping part, he meant that with Starmie's good offensive stats, it can sweep, and help others as a wallbreaker. Starmie's offensive stats that Gen was really great (it's A+; check VR), and I don't think that there was any need to edit this answer, except for the Speed Increase part, which is a buff that the move got this Gen.
And, if you wanted Spikes / Rocks / TSpikes to stay off your field, you would always have to go with the "pitiful base 20 power".
Except the Specs / Scarf set (which really won't be Spinning - that's for a late-game sweep), almost every set recommends Rapid Spin on Starmie. There are also sets which are made especially for a Spinner Starmie.