Does a section 217 election make sense if my only Canadian income is CPP and OAS?

Often, yes. If your only Canadian-source income is CPP and Old Age Security, your total income is likely modest, and a section 217 election lets that income be taxed using Canadian graduated rates and personal credits rather than a flat non-resident withholding rate that applies regardless of how little else you're earning. For someone in that position, the graduated approach can genuinely produce a lower tax bill than the flat withholding already being deducted.

Whether it actually pays off still depends on your full income picture, not just your Canadian income, because the calculation looks at your worldwide income to work out the Canadian tax and credits properly, even though only the Canadian-source amounts are ultimately being taxed by Canada. Someone with substantial income from other countries, even with only CPP and OAS as their Canadian income, may not benefit as much as someone whose Canadian pension is close to their entire income.

Because this is elective rather than mandatory, and because the comparison depends on your specific numbers, running the calculation both ways, with and without the election, before deciding is the sensible way to approach it rather than assuming it will always help simply because your Canadian income is limited to CPP and OAS.