I'd suggest lowering the period, make it 2-3 days instead of 7, this way you will greatly reduce the number of low-priority tracks because they played recently.
Another solution, in addition to (or instead of) reducing the number of days: create cascading rules, for instance:
rule 1 - decrease priority by 10 for tracks that were played 1 day ago
rule 2 - decrease priority by 10 for tracks that were played 3 days ago
rule 3 - decrease priority by 10 for tracks that were played 5 days ago
etc.
The rules stack up if the track falls for multiple rules.
Example. In this case, if a track was played just now, it falls under all rules (1, 2 and 3), so its priority will be decreased by 30. If a track was played 2 days ago, its priority will be decreased by 20 because of rules 2 and 3.