I know that in the future more ways of spending imagination will be added to the game, which is great, and I'm happy to wait for those, but I think as long as things that are added to the game are targeted at average players there will always be those glitchen who end up with stacks and stacks of unused imagination.
Level 60s need to earn a total of 23 million imagination to get there. If a typical glitch player play a few hours here and there then they probably won't earn that much for years and years of real time. As a result, everything that is costed within the grasp of a typical player is going to be dirt cheap to a current level 60, and they will buy it all as soon as it appears.
The "hardcore" glitchen may not constitute a large amount of the community, but I think we have our place. In order to address this issue I think that ultimately there will need to be upgrades or other ways of spending imagination specifically targeted at crazy people who are willing to earn millions a week to pursue foolish goals. In order to qualify it has to be things that we can spend an unlimited amount on but that no one who doesn't play like crazy will miss.
These don't have to take up a huge amount of developer time to implement. For example:
Remove the cap on brain capacity and quoin multiplier but make the price of those things increase exponentially as you go above the current cap (quoin multipliers of 200+ were getting way out of hand, but suppose cards went up 5% per multiplier above 100, then we'd need to drop 2 million to get to 125 or almost 9 million to get to 150).
Add a card, again with an expanding cost (though maybe not exponentially since this card confers very little advantage), that increases the number of items you can transmute or the number of things you can cook at once by 1 for those who already have the existing upgrade. Let people stack that to the moon.
Let people buy up their chance of super harvests at extremely high and exponentially expanding cost.
The trick would be pricing all of these things so that we can never really expect to get our investment back. Imagine upping your tree super harvest by 1% cost 100,000 imagination and increased by 40% in cost for each extra point. In order to get that first point back in value you would have to harvest from around 55k trees, which would be around the amount I typically harvest from in a month and a half. By the time I got to a total of 20% bonus I would have sunk almost 7 million imagination into it - that 10th upgrade would take me about 3 years of play before I got my money's worth out of it (it would be 208 million to get to a 30% chance).
I can see how these kinds of features wouldn't be a top priority, but I some kind of massive imagination nsink will be critical to the long term playability of the game for a small segment of the population.