When I got my commercial I was dismayed to find it had no effect on my insurance. In fact I didn't see much from my instrument either. Besides more hours, about the only thing that has successfully had an impact on my rates was incessant complaining and threats to cancel the policy. I can't imagine it's any more fun for them than it is for me.
The dividend from additional instruction is the increased safety of you and your passengers! While it would be nice for the insurance to recognize and reward that, you should do it for yourself regardless. I flew for years on my own, crawling out from under a rock every 2 years for a BFR and then zooming back into oblivion. I flew fine, but I wasn't getting any better. Then I got married non-aviation lady and had kids. Not knowing any better, they would tell me "You're such a good pilot." I decided I wanted to be as good a pilot as they thought I was. I started training, adding ratings, etc... and quickly found out how much I didn't know.
Get the commercial. It will make you a better pilot. And if they insurance company blesses you with a lower rate, well that's a bonus.
DEM