Is worth accepting to review manuscripts in low quality journals
I think a lot depends on what you define as "low-quality journals". If you mean lower-tier but legitimate journals (typically subscription-based, or free OA) with high acceptance rate and low impact, listing these will have neutral to slightly positive effect. Indeed, someone has to start curating the quality in order for some of these to raise in quality and impact.

If you mean fake, pay-to-publish "predatory" journals then the effect will be strongly negative. By accepting to review for these journals you are encouraging a business that hurts science and scientific publishing. Also, you're wasting your time since these journals will accept papers on the basis of whether the authors paid, not on the reviewers' recommendation.