I guess when the results match the investment? If those statistics are true (I looked it up, I see where it says that, but based on the results, one can only wonder), then either you have a population that has a lower intelligence than all the countries with better educated citizens while spending less per pupil (I personally don't think this is true), or the money that is being spent per student is being mismanaged compared to what other countries are able to achieve. Problematic, no? if the standard is fine, then it doesn't matter what is currently being spent, it's not enough, if your results are so far behind so many other countries, most of who's GDP is a tiny fraction of the US's. If you don't want to fix the process, and you don't want to fall behind the rest of the world, there's a whole bunch of bullet budget that could be reallocated. I think everyone would be happy if you guys spent less on your military...hehe
Bridges to nowhere? No. But I've been in the states, and compared to the roads we have up there, there are a lot of bridges to somewhere that could use some fixing...hehe.... How about: Re-educating people currently in low skilled labor jobs that are disappearing through outsourcing and automation, so they can continue to support themselves and pay into the system? Demanding corporations pay an adequate wage so that governments don't have to subsidize with welfare and food stamps? Incentivizing companies who create jobs with tax breaks that are attractive, but less than the income taxes the jobs generate? Taxing corporations penny for penny for all environmental impacts requiring government expenditure to address? Closing all loopholes, so that corporations cannot continue to make unfathomable profits while not giving their fair share back to the country in which they have become so prosperous? These items don't seem that outrageous to me, and for the most part either cost nothing, or pay for themselves over a short amount of time.
So, when is enough...that's a good question, honestly, and one I find myself asking as a progressive who used to be a conservative.
On the surface it seems like a never ending proposition, but there was a time when being the best was the golden standard, and countries competed to get there. As records were set, records were broken, and out of that came so many innovations, up to and including putting a human being on the moon. So, I guess I have to ask...why should it ever be "enough"? I can't think of any reason why we, as a species, should ever stop trying to do better, and look for better ways to remove hurdles to that endeavor. Reducing prioritization on military strength in favor of education and "welfare" (not hand outs, but the overall welfare of the citizenry, perhaps better said by standard of living), and demanding corporations live up to the same standards of good citizenship as the rest of your citizenry (pay your taxes, don't litter, obey the laws, be accountable, don't steal) are all ways of removing hurdles, and in my mind are the right things to do...and has a far favorable economic outlook than the current stagnation, and indeed regression, going on in the states.