Lowering your weight a bit does impact your ultimate potential top end, but most scoots are barely going to hit that. By dropping it the weight you'll probably hit your actual top end, but the bike may seem kinda wrung out when you do.
Of course TANSTAAFL.
It does increase your RPM, so you do impact gas mileage and likely to a trivial extent engine life as well.
Of these things you'll probably notice the MPG and RPMs the most.
I poked around just a tetch and found
https://www.scooterdynasty.com/variatorrollerweightsfor200ilancescooters.aspx, &
https://get2itparts.com/All-Parts/Transmission-Parts/Roller-Weights-Sliders/634325-CLUTCH-ROLLER-WEIGHTS-SET.
The latter is especially interesting since it cross references the OEM part number from the first and seems to note it as 13g & as the same weight used in the Lance 150s.
So judging by the 13 in their part number I'd guess at 13g as your starting weight. Short of digging around more the easiest way to find out is to simply weigh one of your existing weights.
Far as how low to go. Kinda depends on your end game. I dropped both my HDs 1 gram. Sliders in one rollers in the other. Works great. 2g would be a waste, especially if the drive train is the same one that was OK for the 150 series so it's already a bit bumped up in that regard anyway.
One final note on this. If you move 'em too far you may start getting belt slip, possible breakage, clutch chatter etc.
That would bring you into the world of playing with clutches which can be fun, but is not something I've really gotten into; albeit I've fixed a couple with OEM stuff.
So to sum my thoughts up.
Weigh one of your weights. If it's 13g try 12. OEM clutch 'n stuff should be fine there.
If you really want to play with it you can get something like this (verify your size & order appropriately. Seems to be 18x14 but I didn't do more than glance)
https://www.scooterworks.com/Prima-Roller-Weight-Tuning-Kit-18x14-6g-to-17g-P1936.aspx