Those who tested a decade ago should upgrade. Amazing progress has been made since then. For example, autosomal DNA testing finds cousins (up to about fifth cousins, and less reliably back to about tenth cousins) along all lines, not only fathers father’s father’s line (Y-DNA) or mother’s mother’s mother’s line (mtDNA).
I just had my old 12 marker test upgrade to a 37 marker test.
We've managed to connect this DNA to my sister's geno work and it led us in a different direction than expected.