my agility 50 has 5500 kms and I replaced rollers today and there was no more strange rattle sound
during acceleration, so it's a time to replace it on your's too. I put 6.5 grams
I did it myself (30 minutes job) and I'm weekend mechanic.
Here's service manual to download:
http://rapidshare.com/#!download|252l34|364918903|bmanual.com_Kymco_Agility_50.rar|17984
And you asked what can you do to make agility faster, so I guess you have fully de-restricted scoot(jet, boss drive, cdi).
Expected max speed is about 60 - 65 km/h (at least on mine). cdi is programmed for max 9000 rpm (7500 rpm restricted)
and whatever you do on your carb, exhaust, big bore, etc, will give you more power but no more speed.
For better speed place to look is your variator system(roller weights, drive/driven pulleys, clutch springs, belt and
gear ratio(most efficient in my oppinion).
But thats money pit man. I payed mine 850 eur new and I could easy spend 200-400 eur(almost half the value of the sooter) on quality variator mod. parts for 10-15 km/ speed increase.
You do the math is it worth to invest in such modifications.
I think it's better to buy 125 cc scooter (100+ km/h) with bigger chassis and invest in motorcycle drivers licence.
Don't get me wrong but that's my oppinion and my 65 km/h agility is just fine for me.