The SB +/- 3 hours I mentioned below gradually increased the flakeyness factor by being absurdly late and getting "very busy at work". Eventually I called her out on it and this is what she said: Yes, I'm doing it on purpose. The allowance isn't enough for me. If you increase my allowance I'll go back to my early behavior and pay more attention to you!

Had she asked me for an increase while between the sheets my little head would have agreed, but this smacked of The Art Of The Deal or something similar. I responded politely, basically take it or leave it. Has anyone have this happen?

This is the equivalent of giving a contractor an advance on work not yet done. Once the money is in hand, there's no incentive to complete the work. This is why I will only do a ppm arrangement. I would however follow Gaza's method and break down the allowance according to meetings per month...so these poor little girls don't have to look in the mirror.

but it has the opposite effect on me, when they start acting out like this I simply drop them from my rotation and we never end up having "the talk" like you just had.

 
To be honest, I really am rather easy to manipulate. All a woman has to do is "ask nicely" or even better let me think it was my idea to give her more and I'll cough up the extra money in a heartbeat. I don't really care about a few extra bucks, but I don't like entitled people, I can't stand demanding women, and I refuse to give into passive aggressive behavior like your SB tried to pull on you.

 
Ironically, I had one of my regs "get me" just yesterday for some extra money, but she was much smarter about it. Rather than demanding extra allowance, she mentioned in passing how she was having kind of a rough day because she needed some extra money because of school starting next week, but for me not to worry about it as she could always go pawn something next week. Worked like a charm, she NEVER asked, and when I offered she demurely told me I "didn't have to" do this for her as it was her problem not mine. It wasn't a lot of money, and since she not only let me think it was my decision, coupled with the fact I know she still would have seen me even if I didn't help her with a little extra that she needed this week, I was more than happy to help her out. OTOH, if she had told me that she couldn't see me without the extra allowance i would have dropped her on the spot.  

 
I think you did the right thing. Once you give into this type of "extortion" it never ends and it only gets worse from here. There are simply too many POT SB's out there who will be grateful for what ever help you give them.

This kind of behavior is just not acceptable to me.  I despise being manipulated and I push back, either by pushing her to the back of my rotation, just not being available to her for an extended time, or when it's really egregious just telling her "Bye, Felicia!" (Look it up in the Urban Dictionary...).
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Here's some guidance you can always use to figure out these type of situations:  Who ever has the power controls the outcome.  In the sugar bowl, there are two kinds of power:  cash and pussy. As long as you feel you can get more pussy for the same or less cash, you have the most power. If her pussy is too good to replace (Be objective here! GPS SB's always think their pussy is unique and magical, but trust me it is NOT!) , she has the most power.  In most markets, certainly in Los Angeles (my market) there's literally thousands of POT SB's within 25 miles of me. Not that finding a new SB is ever easy... But the POT SB pool is huge, so it's just a function of time to replace a spot on my rotation.  
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BTW: you may be tempted to try this in reverse by withholding or deducting some percent of her allowance when she behaves poorly (arrives late, leave early, texting on her phone, hinting about more allowance), but this is unlikely to be a successful strategy. She will generally not agree to less allowance then what was promised and she will either continue the bad behavior to try "train" you, or just dump you and move on. Plus IMHO it's kind of an immature dick move.  Part of the appeal of younger women dating older guys is that we are much more mature than their contemporaries. And engaging in a tit-for-tat battle to "get even" with her is just juvenile.  
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So just call her out and let her know it's unacceptable.  If she bails, she would have bailed anyway. If she doesn't, your arrangement is now stronger and her respect for you will increase.  If an SB in my rotation approaches me for more allowance I go back to my original negotiation process:
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Me: Here's my budget  - I offer X allowance for Y time and activity.  
Her: Here's my ask - I offer Y time and activity for X allowance.  
Each can then adjust up or down until there is a meeting of expectations.  
OR either of you can exercise your NSA option and just walk away.  Then it's wash, rinse, repeat with the next POT.

Everything you said here is true, and I've had similar experiences.  When a SB is appreciative of a little extra gift I become sweet and generous..  When she demands it I disappear.

Otoh, when negotiating,  just be clear about what you will or won't do.  It works surprisingly well on occasion. I had a really cute little 19yo thing tell me she couldn't meet me for $200.  She said her previous SDs gave her $500 and that's all she'd consider.  So I wished her good luck.  Turns out she couldn't find anyone decent willing to pay $500, (surprise , surprise) so we had our first date at the $200 I had originally offered.  And guess what?  She loved it, loved the sex with me, and has kept coming back for more.  I gave her a $50 gift card as a bonus one time, and last time I gave her an extra hundred because I knew she needed it.  I happily surprised to see that she's now a regular in my rotation.  So stick to a budget that works for you.

After my take-it-or-leave-it she did actually bail saying that she could make more per hour at work (web graphics or something).  Highly doubtful because she's back on SA every day.  A great pity because she was really exceptional in the sack.  Like I said, had she asked nicely I would have agreed for the sake of her pussy.  

So now it's a dilemma with my No. 2, also Japanese (I'm in Tokyo ). We have no real connection and after she orgasms pretty much goes for her clothes to leave.  Also this one has expensive tastes in restaurants. I'm thinking of dumping her but have no other options. Will have to wait till I get back to the US to my usual SB who, who knows, maybe with someone else by now.