What upgrades really work?
 

My Ruckus is a dirty old nail of a thing that's never had a happy day in her life. This weekend I had to go on a 150km round trip and didn't have anything else to use. She made it there and back with no problems, amidst some of the most hateful, violent driving you can possibly imagine. I lost count of how many times I was literally run off the road by someone driving straight at me on the wrong side of the road.
But she took it all like a pro... Until I got home. I took her out in the evening to get some food and she was rattling, grinding and making sloppy piston and cam-chain growling noises. She is not a happy camper. A swapped the oil out, it wasn't as bad as i feared, but the fresh stuff did nothing to calm her down. She's running OK, probably lost a little power but otherwise she's rumbling on and not making a fuss.
So it looks like I'm facing a re-build which is something I had already come to terms with. I got this bike for next to nothing and figured I'd either clear it out or have to spend money on it. I've decided to keep it so spending money it is!
What really works on these? I'm pretty mechanical but living in a 3rd world country where advice and technical expertise is thin on the ground. I'm thinking of making sensible upgrades that would make her a little better but i can't afford to sacrifice reliability. Parts are just too hard to get out here.
Without breaking the bank, what are the common, trustworthy upgrades to score a bit more power out of these things? I'm already pretty certain I'm upgrading the suspension and brakes, repainting the frame and body and swapping the headlights out for LEDS. I don't want to lower the seat or bars but the seat frame is a bodge thing someone has stuck on before I got her. I'd get a replacement if I could, or might have one made.
I've seen a carb setup for $100 which looks interesting. Is there a bore and piston kit that is recommended?
Any advice is welcome.

Thanks

Re: What upgrades really work?
 

Polini variator kit, Polini kevlar belt, Yoshimura exhaust, aftermarket air filter, along with an NCY perfomance cdi(unlimited revs), these parts work.
There are bore kits available in 58.1cc & 66.6cc, but they are expensive. I have no first hand experience of them, sorry.
There is always the GY6 route(the dark side), but that involves a new engine mount, harness, fuel pump, rear wheel(a donor bike would help)
and alot of swearing. Either way its pretty costly to improve performance on a stock Ruck. I went the GY6 route for the acceleration and cruising speed.

Re: What upgrades really work?
 

sTol2m broke it down pretty well. With that being said, in your situation I'd think a big bore kit would be your best option. It's likely the most reliable option and you're going to need to rebuild the internals at this point anyways. I think its definitely feasible to do a big bore kit for ≤ a gy6 swap.

Even with a new variator kit, belt, exhaust, intake and CDI (~$500+) you might only squeeze another 5-8 mph out of it and you'd still need a rebuilt on top of that. (You would see improvements in acceleration but don't expect too much top end improvement with the stock GET)