What is the importance of good grades?

Hey

Im currently working as a fixed income trader in one of the nordic banks and have a Bsc in business/finance. Before joining this role I did a year of credit sales. The situation is now that I have gotten very interested in programming as well as maths and have decided to pursue this in some different manners. I was admitted to a Bsc in mathematics which im going to try and complete besides my full time job. However, I do have several other "hobbies" and fear that I might not be talented enough to have time for all of this whilst also getting top grades.

So here comes my question: Do you guys think that having gotten "not-top-grades" will be a significant detriment to my overall credentials after finishing these new studies? I realise the question might be silly as either I could have my current Bsc in finance (with very good grades) or I current Bsc in finance (with very good grades) + a Bsc in maths with mediocre grades. And the latter is probably preferable in most cases, but do you think there could be a case where a future recruiter thinks "well he didn't get top grades in his math degree and therefore it doesn't really matter"?

Thanks in advance!