Having reviewed most of the suggestions already submitted, there are quite a few I'd like to second, as well as several of my own. I'm not suggesting all of these be implemented together because some might not mix well. I am suggesting that they are all good ideas.
In no particular order:
1) A GW-specific defense Win/Loss log.
2) Points for defensive wins that increase based on certain criteria (color, non-duplicated troops, erc.).
3) A sliding "complete all" feature to guild sentinels.
4) A high-stakes, locked loadout mode where you must select your troops, can't change them, and then fight your wars. There is a bonus multiplier to doing this to offset the risk.
5) Up to a certain bracket (top 10 brackets perhaps?), only the best 25 scores are counted with the remaining 5 being an average of the 25. More and more player scores are counted as you advance brackets, with all scores counted in the top 1 or 2 brackets.
6a) GW as a 2-week event where you fight everyone in your bracket, and rest days are Mondays and Sundays, with a bonus day where we fight the devs.
6b) Alternatively, 5 battles per week, with the unused 6th color being the buffed color that week.
7) Gain a copy of the week's troop in each victory (or every 2 victories).
8) GW being seasonal (ecample: 4 weeks on, 2 off) with an epic season-end reward based on placement.
9) Reverse sentinel stat bonus for attacking (as many have suggested).
10) Auto-complete option where a player can select an attack team for the day/week and let the AI run the battle.
11) Tier unlocking but not mandatory tier advancement (i.e., a weaker player can choose to just fight soldiers).