When should I stop playing endless mode in Plants vs Zombies?

I don't think there's already a clone question, if there is I apologize but I didn't find it.

It's kinda of a spoiler but not really a spoiler.

So I'm using this strategy and I have 142 flags:

The thing is since flag #50 I'm not noticing changes in the behaviour of the AI. Basically I'm winning easy, I have just to restore the Pumpkin shield on the plants. I really don't care about doing 1000 flags so should I expect some increase in difficulty or is that it?

The version is Game of the Year.

I've searched fairly extensively and I can't find anything that suggests it gets harder.

this guy hit 8000+ flags... so ...

endless is the best way to make money and farm plants/chocolate to you zen garden, you should stop when you get filled with all this stuff.