Well all of the above are designed to keep current players involved with the game and playing it, but even these can get repetitive after a while, and eventually player levels are going to drift down.

So you also need something to bring new players into a game to replace the ones you are losing, and at the same time re-attract those who have drifted away.

With a game like Wipeout you can't really do much in the way of new craft, as there is basically only 4 specs to play with.
Adding new weapons is a double edged sword because you could easily get it wrong and upset the balance of the game, which would alienate more than bring together, besides, both of the options above mean player options, and the more player options you have can make it slower to load if playing online, you could end up waiting half as long for a track to load as the actual race took , and nobody would put up with that.

The only real thing that would keep people happy would be new tracks.
Now I don't mean a whole add on pack like Fury was to HD, more like one new track added say once every 4 to 6 months would suffice, it would give everybody enough time to play it to death and try to be the fastest on it before the next one came out.

This would also keep the studio building the game active in keeping the old one working properly, while designing anything new, plus one track every 5 months wouldn't need a whole team to do it, they could have the basic framework done, and have new designers and Artist that are coming through have a go at it, this would also keep both the game and the people building it fresh, everybody's happy.....well in theory