These items are meant to be extraordinarily rare, so I don't support raising the stock rate, at least permanently. Technically speaking, also, if something stocks at 2,000 RC, and the rate of tu to RC is 300k per, the 2,000 RC items could sell for 600mil, which actually is a good price (imo) for items that were/are still practically retired.
Also adding that not everything is expensive, I think just the rarer ones are. For example, Mark of the Soulless has a base price of 250 RC, which isn't that much more than the base price that the new dye kits have of 200 RC.
I do, however, think it would be cool to have mini events that correlate to 'discounts' on certain items if they happen to stock during that time, such as discounts on items or a higher stock rate for items that were released during events. So for example, maybe it could be that old Halloween event items (like Halloween Attack Apple, I assume that was released during Halloween) could stock higher OR be priced lower during Halloween. I think that might be a bit hard to code though, especially since it's not guaranteed these items would stock.