Nice job. Better tires will certainly help you out. If you feel like your skills are still improving with each event, I'd just stick with what you have until they're worn out. I purposely stuck with my cheap Hankook V12s for all the AX and DEs I've done over the past year with the sole intention of learning better car control. They aren't the grippiest option out there, but they're cheap and I've continued to improve on them.
I just recently decided to upgrade and went with the Dunlop Star Specs. I did an autocross last Saturday and was amazed by the difference. The same guy has set FTD in every AX I've ever done except one, so he's a great benchmark to gauge progress. In the first two AXs I did this year, he beat me by 7 or 8 seconds, and this time it was a little under 4 seconds. Also, the guy who won my class last month beat me by 3 seconds, and this time he just edged me out of 1st by .004 seconds. That's less than 3 inches at speed!
So yeah, hopefully that gives you an idea of what you can do with better tires.
'07 E92 BMW 335i