On the one hand you are complaining that the searches done through Dash are insufficiently targeted.
On the other hand you suggest that Ubuntu should anonymize queries.
This is somewhat contradictory. Anonymized queries generally suffer from being poorly targeted. The more the search engine knows about you, the better it can target its search results. So, in an ideal world, the search engine should have a pretty good profile about you, your interests, and your activities.
At the very least, it should probably know whether you are currently performing a commercial query, or whether you are just looking for a local file. IMHO, this is the biggest shortcoming in using something like Dash to do searches.
And of course, there is always a very legitimate concern that the search engine should also preserve your privacy.