It’s not so measly. Besides, material comfort is only a part of what makes life interesting at this age. The stipend pays basics. If the rent is reasonable, they can even splurge from time to time. They get to interact with great people and enjoy campus culture that money can’t buy. My D is at a top math grad program. Stressful at times but overall she is having a great time. My impression is that reseach experience is the most important part of application to grad school. Participating in REUs are highly recommended. Students can learn how they do in research and if it’s a career they would like. Research isn’t for everyone. They can also see how they compare with others pursuing an academic career. i am guessing kids from the most competitive REUs end up at selective programs. Of course, if they would like to make money during summer, REUs are not for them. REUs pay far less than industry internships mirroring what’s to come. Comparing my D’s REU pay to her friend’s internship pay, I’d say about 4 times less.
About taking grad courses, most kids run out undergrad courses to take in their junior or senior year. At universities they can take grad courses. Most LACs offer a few graduate courses to remedy that. National Research Council ranks grad programs every 5 or 10 years. USNews really doesn’t work for graduate programs.