Don’t know the exact droprates, but since they increased the number of possible blueprint rerolls, they have been dropping like flies from the troves. You also have the benefit of troves having a few set locations (it is easy to check all the spots fast). In the time it takes you to find and kill a single Nemesis, you can do multiple Mountain Deeps runs. There are other convenient troves, but the fastest one I found is in the Mountain Deeps and it has the major benefit of Ikrix always being close to a trove spawn point. Just be sure to have a lot of dynamite handy.
And yes, bonewalls and bonespikes galore. You will be drowning in them.
EDIT:
I would also recommend this - Treasure trove guide - https://steamcommunity.com/sharedfiles/filedetails/?id=660379177
I already memorized the locations so don’t need it anymore but has been very helpful to me initially.
NOTE: There are a few locations missing in the guide, which were probably added in a later game update (Mountain Deeps for example has 4 spawn locations AFAIK).