Rotate the legal card list monthly instead of after each regular set release.
Each rotation, ban the top 1% most played cards for a number of rotations. Or a random number of rotations for each card so they don't all become legal again simultaneously.
Set a limit on the max number of copies allowed of each card. The limit could be randomized each rotation.
Limit the number of rares/mythics allowed per deck.
Require a minimum number of cards from the latest sets.
Have occasional flashback weekends using previous cardpool rotations.
Sometimes change to a different base cardpool like a block format or a format other than vintage.
Ideas to shake up the meta: