If you want an increase in resin production grow better weed, lol. That pretty much sums it up. If the genetics aren't there, the potency won't be. Go put some of that shit on wild hemp and tell me how high you get after a telephone pole sized joint.
Chitosan is what you are looking for. It induces SAR in the plant. It can be used in conjunction with Salicylic Acid or Harpin protien (HALO). I am doin my first run with Harpin Protien in the form of Halo foliar spray. I foliar with the Chitosan every 3 weeks up until week 6. I have seen a slight increase in trich density. What I was really impressed with was tha fact that the table that I treated with the Chitosan was much more resistant to a powder mildew outbreak that the control table w/out chitosan. Dehu broke and had 80% humidity for a couple days. People on this site are so quick to call everything "snake oil" even if they have no hands on expierence with a product. I purchased from them http://www.agrihouse.com/pdf/ODC Brochure.pdf. I have gotten my biggest increases in resin from playing with the enviorment as opposed to a nute additive. Low Temp, low RH for the win!!!