IMHO......it all depends upon how much change you can get your hands on.
If you are struggling like many are.....then it makes sense to do the easy low buck mods first and save for the bigger ones down the road. Buy a UNI air filter, get a KLX needle kit, search out my way of doing the low buck exhaust mod first before cutting up a perfectly good exhaust and ruining it(you can always cut more out but it gets very difficult to go the other way!),.
If that is good for you now, then leave it alone and save save save!....The next step would be 685, then you can do the head in stages or all at once, your call.....it will only cost you gaskets each time......a 685 gasket is $50...so not cheap to ruin and keep replacing, that money can go towards a set of valves or a good shop having a go at it with a die grinder. The 685 will give you a good bang, not great but good....the head will give you the same bang for more bucks, not as good of return on your $$$, BUT....the head is where you will make HP. The engine needs to breath and breath well, so larger valves and a good porting job will accomplish this. You now have what most people stop at. If you can still find some extra change, think flatslide carb......it delivers the air/fuel mixture that the engine wants instantly compared to vacuum operated as the CV carb does. It also gives it a pump too, so you get the best of two worlds, instant throttle responce and a pump to jam that fuel down it's throat. Yes if you insist on using the pump as you will once you get the feeling from it...your gas milage will suffer, but if you learn not to use the pump every time the milages aren't that far off the last stage of the engine set up. I get low 40's with my big engine and when running a flatslide for an experiment on a bone stock 08 engine I got better milages than with the CV carb...mid to upper 50's easily!
It is a hard pill to swallow when it comes to engine building, do I jump in feet first or carefully plan out an attack. Most jump right in....I did and then took it apart many times doing things as I saw fit. I have wasted many $$$ doing it this way. Then comes cams....another $500 by the time they are installed....but when added to the above engine it will allow this engine to scream past redline and pull all the way there. Yep, I love it!!!
Think about how fast you can save the money and then do things as you can without wasting money.....seriously it is the best way.....almost impossible to do, but the best way.