I think it would be great if you could tell whether an item is big or small before buying or preparing it. Inventory management is is a critical part of the game and inventory slots are scarce. Some kind of visual difference in the item panel - an extra symbol, different font color, different background color for the item name panel - anything to let you tell at a glance whether an item is big or small would be nice to help you plan better when confronted with an unfamiliar item.
On that note, have you considered making alchemy shops available in a dungeon? The Compression Seal is one of my favorite items, but it's fairly difficult to leverage the advantage it gives with just one of them. I'd like to be able to spend gold inside a dungeon to buy a Compression Seal and free up room for more items.
I don't think there is much potential for abuse of the Translocation Seal being available to buy inside a dungeon. Its price being as prohibitive as it is, you could only profit off it on a small number of items, and not by a lot on those. So the Transmutation Seal might be the only obstacle to making alchemy shops available during dungeon runs, as far as balancing goes.
Making one or several alchemy shops available in dungeons could also be made a preparation you could buy from Bezar, similar to Apothecaries.
Also, have you considered making lockered items remember their size? I think it would be neat if you could use a Compression Seal on an item, locker it, and have it be a small item when you prepare it. Balancing might be an issue with that, though.
Let me know what you think of these ideas!