I agree about the loss of groups because creators/store owners/managers have to join groups for events/hunts/sales. Not every creator is a Premium account. I buy more L than I would get from a stipend so I never went Premium. The land price drops don't help me at all since I have a homestead that I rent.
The message cap is a big kick in the teeth. Yes, messages go to your email so you can still read them offline. That doesn't help with stuff dropped on you. I own a weekend sales list. I use a dedicated sale alt for the group. I give merchants a dropbox that they rezz, grant debit, put their submission cards in and hit send. Saves them fighting to make TPs or lag. All convenient in one spot, their own land. This does not count as a notecard being dropped on you so it isn't automatically saved if you cap. Merchants message asking questions, shoppers message to let us know if something is wrong, subscribers send you new subscriber messages. A cap of 15 means at most 7 cards and one message of some kind because the sender also sends us transaction information.
I don't need a house on an alt that stays in the office. I don't need a stipend on her. She only needs 2 groups so no incentive there. There is no reason I would make her a Premium account. Notecards and messages will be lost. Myself or my assistant will have to try to track down cards from merchants that are on the other side of the world and don't keep the same time as we do. The cards might not get replaced before list deadline....especially if the merchants are constantly getting capped due to new limits.
I talked to someone that owns another sales list and she has the same worries. We will need to keep those alts on constantly to make sure we get everything.
You say that this move isn't to punish basic accounts or make them turn Premium but it is doing that anyway.