Can a DNA results from a saliva test be used to more accurately identify ancestry?

I’ve used 23andMe – well, more accurately, my brother has.

I’m not really sure what you mean by “narrow down ancestral origins”. That 40% German/French thing is the narrowing down of your ancestral origins.

If you’re biologically male, you will be able to separate your results into maternal- and paternal-line origins. That is why we had my brother do the test.

This is our broad result, and Here is our separated paternal/maternal line haplogroup results. It shows that our father’s haplotype is consistent with what we were told about his heritage – that he comes from Ireland. Maternal haplotypes are harder to nail down, but we did at least get “Northern Europe” out of it. When I’ve searched for other people with the T2a1a haplotype I’ve found everything from Ireland to Sweden to Poland.

GEDmatch I have not used it myself but there are supposed to be some advanced tools for this. My 23&me basically just confirmed what was obvious:
99.8%European
37.7%British & Irish
25.6%French & German
2.0%Scandinavian
30.5%Broadly Northwestern European

I’m a white guy…. duh.