1. I would add more items to the shop that could be purchased with coins.
Right now there is nothing worth buying whatsoever in the shop - nothing to "work for"
The game would be a lot better if you could buy either cosmetics for your character or if you had some sort of "house" (I'm picturing just a little clearing area similar to the original Pikmin - pic related)
There could be all sorts of items that you could 'decorate' your house with that cost coins. It would give something to work toward / reason to get coins.
2. After adding cosmetic / house decoration rewards, they need to make flower planting cumulative for the day (where you can stop / swap to a different flower color and it still counts to the 500 count) and also lower the number of flowers planted to receive coins - imo it should be closer to 300 (the top rewards should still be in the thousands of coins)
3. Increase the rewards for blue fruit from Big Flowers. For some reason Big Flowers will only give you a single Plum, which is 10 blue nectar
Unless you're releasing Pikmin for their 10 blue flowers, you're always going to end up either very much in the negative or flat from planting blue flowers around a Big Flower
4. Make it so that when you reach a certain level that the fruit your Pikmin can pick up have a chance of giving Pansy / Tulip nectar - shouldn't only be the base nectar forever
5. A much larger bonus for giving colored flowers to Pikmin for challenges. Right now a fully friendship Pikmin gives 20 points - when you give it a flower, 21, if the color is the correct color to the challenge, 22 points.. that is fucking terrible. You should get more than a 5% bonus for having the correct color.. Imo it should be closer to 30 point value total. Right now, there is very little incentive to use pansy / tulip nectar on Pikmin to boost them for challenges (unless you're already collecting the petals from that nectar anyway)