Nothing wrong with the, "if it ain't broke" approach but if you chose to make performance upgrades then now is a good time to do it if you have it apart already. As far as what upgrades to make it really depends on what aspects you want to improve.
Most people are concerned with range and accuracy. For this you want to improve your compression and your hop-up and hop-up rubber. Do a compression check and see where you could be leaking. Does your cylinder head have a double O ring? Does your nozzle have an O ring? These are things that may be worth upgrading. You might also want to try a new style hop system. One of the new flat or bridged style nubs that are on the market now, maybe a shredders type nub. Alternatively you could stick with your traditional style nub and get a firefly or PDI W-hold style rubber.
You should get your gun below 400 FPS as that is the common max allowed for outdoor games. No guarantees but an M110 should do the trick. I like to put bearing spring guides in mine it makes them run smoother and gives me better battery life. A re-shim is usually always a good idea it has many benefits.
Your motor is fine to me with an M110 spring unless you want to increase ROF, but there are other ways of doing that too. Unless your piston shows signs of wear it's should be fine unless you increase ROF in which case you may want to switch to a full metal rack.
Sorbo pads are a nice addition and will help you correct your AOE. Just be aware it's not as simple as just dropping the pads in, you will probably need some custom modification such as shaving down a tooth on your piston.
It all really depends on how far you want to go with it. What I would recommend for you being as it's your first time opening a mechbox is: Clean and re-lube it, Check your compression and correct any poor seals, re-shim and a PDI hop rubber, making sure the rubber is lined up straight when you install it. Other than that just make sure you remember how everything goes together and don't lose anything. Keep your stock parts around because if something decides it doesn't want to work with your set-up you can always go back to the last known working configuration.
Last edited by Kozzie; December 3rd, 2012 at 12:09..