I posted a few ideas on how to encourage weekly changes in defence teams in these threads:
Variety in all PvP, and especially GW, would be a great addition to the long term appeal of the game. Even the most devoted fans get tired of playing two or three teams in every match…
I dislike the ideas of boosting troops or rewards based on frequency / infrequency of use. That feels artificial and probably leads to weeks of random crap, and ages studying this week’s unfashionable bracket to see what could almost make a team there.