Agree with you in principle, particularly in relatively professional environments. Restos are happy to put you in a private room - provided they have one available, and you inform them of your intention to camp out for the evening. As a server, there's nothing worse than campers if you're trying to turn tables and get your slice of the second seating. As a manager-owner it's infuriating and one of those times when the customer is NOT always right. You're not. I know people have special moments they want to share and prolong. The camping privilege costs dollars. Hell, you can't even pitch a tent for free in the great outdoors. Pony up or...do as @Andrew0409 says.
However, they shouldn't even allow it in coffee shops. My good friend owns a cafe-slash-breakfast-slash-lunch place that originally started out as a 7-to-11 coffee shop cafe. She had major problems with campers; people coming in for a 69NT breakfast burger and cup of coffee and staying all fuckin' day. During the busiest times you couldn't get a table cuz of the squatters. She couldn't kick them out; at least she wasn't willing to put her foot down. A lot of 'em were regular faces on the block.
Anyway, what she decided to do was cut the nighttime hours and start closing in the late afternoon. In the meantime, she raised prices (slightly), and that scared off the shit pigeons. Of course, the void was filled by new shit pigeons in time. She's now at the point where she will say to somebody, "Look, the lunch rush is coming and I need that table." Her main business partner is far more brusque about it. Which is neat.
Now, I completely understand the rationale behind the Taiwanese penchant for camping out in every available spot. If I lived with four floors of my family, I'd never go home. Meanwhile, most people want to get out of the house sometimes. Nothing to do in the concrete box except watch TV. At least at the ole MOS Burger, they feel like they somewhere.
So I believe a minimum expenditure policy is a slightly more polite way of telling squatters to make haste. This is a business, not a library. Either you spend 150NT upfront, or choogle your ass down to the park.