In the end decision has to be yours!
https://blog.forumias.com/to-attend-foundation-fc-or-not-for-selected-candidates-not-clearing-prelims-writing-mains/
I would like to add another benefit from the perspective of a student doing self-preparation. The study routine is not consistent for people who do self-preparation. We try to study as per our mood, availability of materials and advice of toppers. In the process, we feel we know something about everything yet there is a feeling of emptiness. We do not have notes ready neither are we able to complete the syllabus. FC can help in these two aspects. Thereby, having completed the syllabus and consolidated notes will definitely boost confidence.