Good points however I think there are niches in everything. For instance take football - you can have discussion about only a certain type or way of playing football and that becomes a niche if you can find enough people interested.
I have been reading that a lot of people that get online do not surf for stuff anymore, they target their time so you will have to source your customers if you want traffic.
You know what, its sites that have been years developing that are doing more than the ones that are just coming on the stream so its hard to get into a good niche now.