I'm not buying gems and I'm barely spending gems because the prices are insane. BB wants to make money in big chunks and that scares away a lot of potential buyers.
I have saved up 7k gems now, because I think all things in the merchant are overpriced or not useful enough for the amount of real money required.
Because of the high price I want to maximize the usefulness of premium, ergo doing lots of adventures. I play this game everyday, but I don't have the time to be online much on weekdays. So the usefulness is very low on weekdays. I'm not spending 800 gems for a week of premium if can only make use of it 2-3 days effectively.
However
I would burn through my 7K gems in a year or less if I could buy 1 day of premium for 100-125 gems. (Or 12 h for 60-70 gems)
And after that I would be very much tempted to buy additional gems.
An other option would be to cut the price of gems and/or the in-game prices with 50-80%