akblack,
Good choice. I have a 2007 and for a simple dual-sport, you can't go wrong. We also use ours when camping to go places the truck won't go and have no problem 2-upping on most trails - the wife is fearless. Likewise, being street legal allows us to get to and from trails and travel in between as necessary and while not a power house or as off-road capable as other bikes I have had, it's a decent compromise for exploring and allows 2-upping. Most XR's get modified during their lifetime so some of the mods I am recommending may already be done on yours. If stock, following would be my list of priorities:
If you are not familiar with advrider.com, I suggest going there, look under thumpers and then under the XR650L thread.
Basic Mods:
Decork and jetting. First order of business is to remove the smog gear and add block offs if not already done. The XR's in general come from the factory lean and need to be rejetted. Do what is known as "Dave's mods". You can find the instructions for decorking and Dave's mods at various places on the world web. These mods are not necessarily just for power improvement but to get the bike running better, cooler and often better gas mileage. But if doing it just for more power is wrong, I don't wanna be right.
Foam airfilter (UNI or K&N are popular choices)
Aftermarket silencer - since you are getting more air and fuel in, a less restrictive (and lighter) silencer is beneficial. I'm still running the OEM however and whatever I choose will have to be as quiet (personal preference).
Tires - since most of your time is off-road, a good set of knobbies are in order if you still are running DS tires - Dunlop 606's are a good choice.
Handlebars - The stock handlebars make for poor ergonomics. I switched to Renthal "CR high" models - I'm 6'2" and allows for a decent standing/riding position. Some people go with risers but I found the stock bars have a strange angle back as well as being too low. Some people find bars and risers to best fit them.
Accessories:
Handguards - Scrap the handguards for bark buster-type guards - save the digits.
Rack on back - If you want to carry more gear, there are various racks available - beware load limits and know that if you want to load it heavy, a subframe mod/reinforcement should be considered - XR's are known for a weak subframe if using your XR as an expedition tool.
Oil cooler - a common mod as air-cooled XR's want to run hot at times - several configurations available - all fairly equally effective.
Maintenance:
Keep clean oil in it
Read up on how to do a CDI repair and/or buy one to keep with you (known common XR650L problem). At a minimum, learn where the CDI unit is so if you are in the wild and it won't start, a light ********** on it with a wrench while running the starter may save you a long walk back.
Other than that, they are a very reliable machine with reasonable treatment. Enjoy!