Here's some silly ideas I had, attempting to balance both being profitable and improving player experience.

ADS

Do not add mandatory ads, but add more optional ads. Potential idea to monetize it further would be doing what some games do now, having an upgrade you can buy for money that skips all optional ads. This gives paid players more stuff to buy, free players more rewards which we desperately need, and also helps to gain more revenue from free players

PVP

You know what would be both a cool feature and something for whales to spend all their money on. PvP! Maybe it could be in a set of leagues like Arena in PvZ2, but not be like PvZ2 and have actual player-vs-player combat. Perhaps vs mode, or a mode where you're both defending your own lawn while attacking the other's lawn? Another thing similar could be doing what PvZA did, and allowing us to attack each others' towns

COMMUNITY LEVELING

Allow our communities to level up and unlock perks, like other games. How does this help monetization? Well, obviously a community full of whales is going to progress much faster, and it could encourage other people in the communities to spend money. I think these should be small perks, like more members, and *slight* buffs to your plants. Maybe a stronger buff the leader can activate but only one can be active at any given time?

COINS

Please, do ANYTHING with coins. You have an entire currency, but it's so useless and plentiful that it's practically impossible for players to spend it, meaning it adds nothing to the game and it fails to make any money. Maybe costumes could be added that cost coins, and perhaps we could donate coins to communities? Daily coin offers? SOMETHING to spend our coins on

UPGRADES

Maybe we could have upgrades like PvZ2. I'm sure you guys could find ways to monetize this, like renting upgrades or upgrade leveling (having extra seed packet levels instead of having multiple of the same upgrade)