Having applied for MPA at SIPA (with zero economics courses), I can let you know in a few weeks whether they matter or not.
Anyway, with your kind of experience, I'd say economics courses would definitely strengthen your chances, and since you have time before you apply, why not go for it? SIPA's application process does not require applicants to submit a SOP, where you could talk about your quantitative credentials and familiarity with economics. They do however need a Quantitative Resume, where you'll need to enlist quantitative and economics courses. In that case, completing a few courses in econ/statistics would establish your familiarity with the concepts. Though, it also depends on whether your undergrad/grad major was a quant heavy topic. Mine was Electrical Engineering, and we do a hell lot of mathematics, so I'm hoping it counts to some extent.
With regards to whether a community college course would be counted, I'd say why not? But you'd better check it once with the admissions office before enrolling.