The primes one is my least favourite one indeed, I left it in just because I happened to include it in the very first version and I am thinking it just counts for 5% in the end...
The regex ones are "micro" yet quite important, dkbench it's a Perl (and C)-based benchmark (reflects our main code), and the regex engine is the most highly optimized part of the language so regex speed is a good representation of text processing speed in Perl.
As I said, the overall score correlates well to SPEC/Geekbench so as a suite it works well.
For compiler comparisons I usually compile a language like python or perl as a test, but I did not want to add something like that, to keep it fast with many smaller benchmarks.