A new barrel is pretty much a must for the spyder, as the stock barrel sucks. Good barrels include the j&j ceramic and Smart Parts Progressive, my 32 Degrees whisper isnt bad, i bought it second hand on the cheap.
Air is a pretty great upgrade as it keeps your velocity more consistent, and it is handy to have a spring kit just incase its too low or too high (out of the box my spyder was shooting 350)
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a new barrel / air / electronic hopper are prolly the main things. Then if you are serious you can start thinking about a new gun, although spyders are pretty great for recball. I put a supa-fly delrin bolt in my spyder, which is pretty mint.
I think the victor isnt electronic, so you could get an electronic trigger (handle replacement for it) i dont know how much they are but its either smart parts or 32 degrees that do them, kingman also do the official ones, but they are pretty much all the same.
hope that gave you something to think about.