With all that power.... how about tires and maybe rims? You could get a set of rims (maybe lighter) and sticky summer tires. Keep the stock set for winter depending on your location. If you have a dedicated winter setup, then sell the stocks or store. Suspension could be next. Also maybe an oil catch can? That's worth about 2.5 horsepower! (just kidding) Not for "performance" really but could help with long term reliability.
With the list you have, you've done most of what's available for the Accord I think. It's hard to come up with more options for raw performance. Well, hard for me to. Good Luck.