Are gems useless?

There are several plants that are offered for purchase with Gems, but it's always limited time offers.  You have to keep checking for them to show up in the store.

Homing Thistle, Hurrikale, Fire Peashooter, Lava Guava, Shrinking Violet, Squash, Jalapeno, Hypnoshroom, Pea-nut, Ghost Pepper, Sweet Potato, Dandelion, Squash, Torchwood, Imitater, Starfruit, Shrinking Violet.

I think I have everything but the Starfruit (I'm playing Tapped Out right now and can't check).

because this game needs financial support

and some plants offered in gem currency in the past. some still offered in gems until now (im not sure though, because i have bought any available plants in gems so i cant check it)