Should I upgrade from 8GB to 16GB of RAM if I keep many browser tabs open?

Yes, upgrading from 8GB to 16GB will noticeably improve multitasking with many browser tabs. Modern browsers are hungry—Chrome alone can eat 500MB-1GB per tab. Eight gigs gets eaten fast, causing swapping to disk and slowdowns. Sixteen gigs gives enough headroom for 20-30 tabs without that pain.