I'm doing a turnover (not profit!) in my Shop on Ark in 5-20k/month, and do not think that Shops is a waste of money. Shop makes a profit, sometimes even more than the some abandoned/empty LA's on Caly, with less investment. I've been selling this Shop for how much I bought it, because I needed money.
On the contrary, I would invest money in the Shop on Rock, because I think the Shops is one of the best and most profitable investments in this game, unless of course you are willing to work in it.
But this is my opinion, and I do not impose it to you, and my Shops work successfully, thanks to my supply management and advertising. I am grateful to all my customers and buyers for their choice, and try to be helpful to them, and...not without benefits for myself. I already wrote that if the Shop stock is a piles of shit, there no one will buy anything, even if it is in the center of the world. Therefore, the Shop is worth as much buyer is ready to pay for it, and depending on the they plans of who he/she pays. Given what I know (and conjecture), but do not intend to write here (let it will intrigue), I do not want to sell my shop on the Next Island for low price. And don't advise to do that to others NI shop owners.