Installing a CAI and exhaust will help, slightly. An engine is basically an air pump; the easier the air can get into the engine and out of the engine without restrictions the more power it will create. That said, the engine puts out 250 hp on an engine stand without any restrictions installed which are there now, at the end user. These restrictions are air filter, silencer prior to the throttle body, and exhaust, minus headers. In the current form; installed in the vehicle, the engine puts out approximately 170 whp. Installing the K&N air intake, according to dyno results, will increase to 180 whp. http://www.knfilters.com/dynocharts/57-3515_dyno.pdf
Not substantial but worth mentioning.
Installing a new exhaust, if possible depending upon where you live, CA I would not do this but I no longer live there, take the J-Pipe off and have a muffler shop or yourself, if you are so inclined and have the tools, redesign as RV6 performance has designed for other Honda models. The factory J-Pipe is very restrictive. I would imagine that you would pick up maybe another 10 or 20 tops whp by removing that, along with the rest of the exhaust, and installing a free-flowing exhaust. It would also be lighter.
The ECU from the factory is tuned for "all" people because they cannot know how an individual person will operate the vehicle. That said, the RL computer is of a solid state design and does not allow for a "piggy back" chip to be installed as on older computer designs. Your ECU would greatly benefit by remapping from a reliable dyno person. These are sometimes expensive ~$400 or more. What they do is they remap the fuel so that excess fuel is not dumped into the cylinders. Richer burns means less likely-hood that an engine will burn up from a lean mixture. Of course the dyno operator will need to know how you drive, typically, what your intended purpose is, and what modifications you have. This is where you will see the most improvement in HP as this will increase the stock 250 hp. I have seen somewhere, cannot find it right now, but they lean out the fuel but still in a safe level so you won't burn up the engine. This is where you will see large increases, maybe as much as, they claim 50 hp. One guy here on the RL forum did this and had dyno numbers to show that as well. Of course that was with the CAI and exhaust. Mileage will increase but I would only guess around 2 mpg, maybe 4 with everything. In the long run, if you keep your truck, worth it at least in my opinion. I am doing my exhaust by the end of this year and then the computer next year as I don't have tons of extra money to throw at my RL. It works superbly but I always want more.